JPH0119247Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a braking device for a reel stand in a magnetic recording/reproducing device such as a tape recorder.

In a tape recorder, which is a type of magnetic recording and reproducing device, a moderate backing is required to ensure that the tape always adheres properly to the magnetic head during recording and playback, and to prevent the tape from becoming loose during tape fast forwarding or fast rewinding. It is necessary to apply tension, and furthermore, when stopping, it is necessary to apply brakes to the reel stand to appropriately stop tape transport. Therefore, during recording playback, fast forwarding, or fast rewinding, a moderate braking force is applied to the reel stand on the supply side, and when stopping, braking force is applied to both the reel stands on the supply side and the take-up side. ing.

However, conventional reel stand braking devices cannot adequately handle devices such as video tape recorders (VTRs) that require extremely weak braking torque to extremely large braking torque depending on the operating mode. . That is, in each operation mode of a VTR, such as recording, playback, and picture search, 20 to 30
While a weak braking torque of around g.cm is required, a strong braking torque of 500 g.cm or more is required when stopping, but with conventional devices it is not possible to freely obtain such a wide range of braking torque. I couldn't do it.

An object of the present invention is to provide a reel stand braking device that can obtain a wide range of braking torque from weak braking torque to strong braking torque through simple control.

The present invention will be explained below with reference to illustrated embodiments.

In FIG. 1, reference numeral 3 indicates a reel shaft, and this reel shaft 3 is provided integrally with the iron core 5, passing through the fixed iron core 5 of the electromagnetic device having the coil 4. The coil 4 is wound around a coil bobbin 6 into which a fixed iron core 5 is fitted and fixed. The electromagnetic device is integrally surrounded by the case 7, and the bent portion of the upper end of the case 7 is screwed to the board 1 of the tape recorder, so that the electromagnetic device is fixed to the bottom of the board 1. ing. The electromagnetic device has a movable core 8 above the fixed core 5 that can move up and down along the reel shaft 3. The upper end of the fixed core 5 is formed in a conical convex shape, and the lower end of the movable core 8 opposing this is formed in a conical concave shape, such that the convex end of the fixed core 5 is shaped like the concave shape of the movable core 8. It penetrates into the end with an appropriate gap. A vertical groove 8a is formed in the movable core 8, and the protrusion 6a of the coil bobbin 6 engages with this groove 8a, thereby preventing the movable core 8 from rotating. There is a lid 9 on the open upper end of the case 7.
is placed on the case 7, and an appropriate number of bent portions 9a are engaged with the case 7, thereby fixing the case 7. A disc-shaped movable plate 10 is loosely fitted to the upper end of the movable core 8, and a nut 11 is screwed onto the upper end of the movable core 8.
It is prevented from coming off by. The nut 11 is configured to be located within the central recess of the movable plate 10, thereby preventing the overall height from increasing. Also, Natsuto 11
The lower end surface of the movable plate 1 is formed into a spherical shape.
Since the movable plate 10 is loosely fitted into the movable iron core 8 with play, the movable plate 10 can be tilted relative to the nut 11.
A repulsion spring 12 is interposed between the movable plate 10 and the coil bobbin 6, and the elasticity of the spring 12 causes the movable plate 10 to be pressed against the nut 11. The movable plate 10 is prevented from rotating by engaging with an appropriate number of protrusions 6b rising from the coil bobbin 6, and an elastic friction material 14 is fixed to the lower surface. As the elastic friction material 14, a nonwoven sheet made of a mixture of polyurethane and nylon, synthetic leather, felt with a small friction surface area and a large thickness, etc. can be used. A friction plate 15 is provided below the friction material 14 so as to be rotatable about the reel shaft 3.
A friction material 16 such as felt is provided below the friction plate 15, and this friction material 16 is fixed on the lid 9 of the electromagnetic device. A ring 17 is fitted in the center of the reel shaft 3 to prevent the movable plate 10, nut 11 and movable iron core 8 from coming off due to the elasticity of the spring 12. The upper half of the reel shaft 3 projects above the substrate 1, and a reel stand 18 is rotatably fitted into the upper half of the reel shaft 3. Further, a reel protrusion 19 is rotatably fitted to the upper end of the reel shaft 3. The outer circumferential portion of the lower end of the reel raised portion 19 is fitted into the inner circumferential portion of the upper end of the reel stand 18 so as to be integral with the inner circumferential portion of the upper end. Reel stand 18
A reel pawl 20 that is to be engaged with an inward protrusion of the tape reel is fitted onto the outer circumference of the upper end, and is prevented from coming off by a reel protrusion 19. The lower end of the reel stand 18 is formed into a large-diameter cylindrical shape, and covers the mechanical part consisting of the movable plate 10, the friction plate 15, etc., and the center of the friction plate 15 is When the position is determined, an appropriate number of protrusions 15a protruding from the outer peripheral surface of the friction plate 15 engage with the axial notch grooves 18b of the reel stand 18, so that the friction plate 15 rotates together with the reel stand 18. ing. Reference numeral 33 is a terminal plate of the coil 4. The reason why the friction plate 15 is positioned using the reel stand 18 as described above is because
The reason for this is to prevent the center position of the friction plate 15 from being deviated from the center position of the reel stand 18 itself.

Now, assuming that the illustrated reel stand device is a tape supply reel stand device, in a mode such as recording/reproduction, a predetermined relatively low voltage is applied to the coil 4 provided under the reel stand 18 to fix it. The iron core 5 is magnetized and the movable iron core 8 is attracted by the fixed iron core 5. When the movable iron core 8 is attracted, the nut 11 is lowered together with the movable iron core 8, and the movable plate 1 is moved by the nut 11.
0 is pulled down against the elasticity of the spring 12, and the friction material 14 is brought into pressure contact with the friction plate 15 rotating together with the reel stand 18, and the friction plate 15 is also brought into pressure contact with the friction material 16, so that it is fixed on the reel stand 18. braking force will be added. As a result, a predetermined back tension is applied to the tape during transportation, so that the tape always adheres well to the magnetic tape, thereby preventing problems such as dropouts. At this time, even when the parallelism between the friction material 14 and the friction plate 15 is not achieved due to the inclination of the reel shaft 3, for example, the chamfer of the nut 11 and the gap between the movable plate 10 and the movable iron core 8 Since the movable plate 10 is tiltable due to the backlash, the friction material 14
When the members 14 and 15 are brought into pressure contact with the friction plate 15, both members 14 and 15 are securely brought into contact with each other over the entire surface, and an even and always stable back tension can be obtained.

Next, if you operate the stop button in recording playback mode, fast forward or fast rewind mode,
At the same time as cutting off the power supply to the drive motor, a high voltage is applied to the coils 4 at the bottom of both the left and right reel stands having the same configuration as shown. As a result, the fixed iron core 5 is strongly magnetized and the movable iron core 8 is strongly attracted to the fixed iron core 5, and the friction material 14 of the movable plate 10 is strongly pressed against the friction plate 15 to generate a strong frictional force, which causes the reel to A strong braking force is generated on the platform 18. Moreover, in this case, since braking force is generated on both the left and right reel stands, both reel stands are reliably stopped and the tape is prevented from loosening.

Here, assuming that the friction material 14 is a rigid body, the moving distance of the movable core 8 and the movable plate 10 based on the magnetization of the fixed core 5 is constant regardless of whether the voltage applied to the coil 4 is low or high. Therefore,
At that time, the gap width between the fixed core 5 and the movable core 8 is also constant, and as a result, only the voltage applied to the coil 4 contributes to the strength of the braking force. is difficult to obtain.

However, according to the present invention, since the friction material 14 is made of an elastic material, a high voltage is applied to the coil 4 compared to the gap width between the iron cores 5 and 8 when a low voltage is applied to the coil 4. Iron core 5 and iron core 8 in the case
The width of the gap between the two becomes smaller by the amount of pressure on the elastic friction material 14. Since the strength of the magnetic field is inversely proportional to the square of the distance from the magnetic pole,
When the applied voltage is increased, in addition to the enhancement of the attraction force due to the increase in the applied voltage itself, the attraction force is increased due to the narrowing of the gap between the iron core 5 and the iron core 8, resulting in an extremely large attraction force. This results in an extremely large braking force. To explain this with reference to FIG. 2, curve _A in FIG.
Curve B shows a similar relationship when a voltage _V2 several times higher than curve A is applied to coil 4. It is. Now, when voltage V ₁ is applied to coil 4, the gap width between iron core 5 and iron core 8 becomes χ ₂ , and the attractive force at that time is y ₁ . Next, considering the case where a voltage V ₂ is applied to the coil 4, if the gap width between the iron core 5 and the iron core 8 is χ ₂ as before, the attractive force y according to the increase in the applied voltage is You should get ₂ . However, according to the present invention, since the friction material 14 is an elastic material, the gap width between the iron cores 5 and 8 becomes smaller due to the strengthening of the suction force, and if the gap width at this time is χ ₁ , then the suction The force is _y3 , which is larger than the suction force _y2 , and a larger suction force is obtained.

Note that the attractive force or braking force based on this when a certain voltage is applied to the coil 4 is affected by the gap width between the iron cores 5 and 8 and the elasticity of the spring 12 in the state when the coil 4 is excited. By adjusting the nut 11, the gap width between the iron core 5 and the iron core 8 is adjusted in advance so that an appropriate suction force can be obtained.

According to the illustrated embodiment, the diameter of the friction mechanism is so small that it is completely surrounded by the reel stand 18. This is achieved by reducing the weight of the movable plate 10 by reducing its diameter.
By making it possible to reduce the elasticity of 2,
This is in order to be able to effectively obtain the attractive force due to the excitation of the coil 4 even when a low voltage is applied, and also to be able to obtain a stable frictional force regardless of the mounting orientation of the reel stand. It is.

Further, in the illustrated embodiment, the lower surface of the loaded tape cassette is connected to the stepped contact surface 18 of the reel stand 18.
At point a, the reel hub is rotationally driven by the engagement of the reel pawl 20. At this time, due to variations in cassette dimensional accuracy, etc., the reel stand 18
Even if the position of the friction plate 15 in the axial direction changes, the friction plate 15 will only be displaced by the notched groove 18b of the reel stand 18 relative to the protrusion 15a.
5 does not move, so the characteristics of the frictional force do not change.

According to the present invention, since the friction member that is pressed against the friction plate by electromagnetic force is made of an elastic material, when the voltage applied to the electromagnetic coil is changed, not only the attraction force changes due to the voltage change itself, but also The width of the gap between the fixed core and the movable core changes due to the change in the suction force mentioned above, and the change in the suction force based on this also acts synergistically, so it is possible to vary the suction force over a wide range from small to large suction force. I can do it. Furthermore, since such changes in the attraction force can be made only by controlling the voltage, control is also easy.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional view showing an embodiment of the present invention;
The figure is a characteristic curve diagram of electromagnetic attractive force for explaining the operation of the present invention. 3... Reel shaft, 4... Coil, 5... Fixed iron core, 6... Coil bobbin, 8... Movable iron core, 10
...Movable plate, 11...Nut, 12...Spring, 1
4...Elastic friction material, 15...Friction plate, 18...Reel stand.

Claims (1)

[Scope of utility model registration request] A reel shaft that rotatably holds the reel stand, a fixed iron core fixed to the reel axis, a coil wound around the fixed iron core, a movable iron core that can move coaxially with the reel axis, and the reel stand. A braking device for a reel stand, comprising: a friction plate to apply a braking force to the rotation of the reel; and a movable plate connected to the movable iron core and having an elastic friction material on a surface facing the friction plate.