JPS5839271B2 - Rotational force transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotational force transmission device suitable for application to, for example, a rotating magnetic head device of a VTR.

For example, in a rotating magnetic head device of a VTR, when the upper drum of the magnetic tape guide drum is rotated by a motor, there is a gap between the pulley of the motor and the pulley of the upper drum to which the magnetic head is attached. This may be done by stretching the belt.

Normally, this motor rotates the upper drum at a certain constant rotation speed, and a brake servo is applied to the upper drum to reduce the rotation speed appropriately, thereby rotating the upper drum at a constant rotation speed. I try to control it.

Now, a curve 11 in FIG. 2 shows the change in the rotational speed of the upper drum with respect to temperature when the brake servo is not applied to the rotation of the upper drum.

That is, according to this curve 11, it can be seen that the rotation speed of the upper drum decreases as the temperature decreases.

For example, this motor is at room temperature t.

It is assumed that the setting is such that a substantially constant rotational speed R6 is obtained at (=259C).

In this way, when the temperature drops to about 0℃, for example,
The rotational speed may drop suddenly and deviate from the permissible range.

Although it is not clear why the rotational speed of the upper drum, which is the rotating drum of the magnetic tape guide drum, decreases due to such a temperature drop, the main cause is thought to be that the grease on the bearing hardens due to the temperature drop. .

Moreover, this tendency becomes even stronger especially when the motor is subjected to other types of mechanical loads.

In view of this, the present invention relates to a rotational force transmission device that transmits rotational force by stretching a belt between a bobber of a rotational drive source and a pulley of a rotationally driven body, and particularly relates to a rotational force transmission device that transmits rotational force by stretching a belt between a bobber of a rotational drive source and a pulley of a rotationally driven body. The purpose of the present invention is to propose a system that can compensate for changes in the rotational speed of a rotationally driven body due to

An embodiment in which the present invention is applied to a rotating magnetic head device for a VTR will be described in detail below with reference to FIG.

In FIG. 1, reference numeral 1 denotes a magnetic tape guide drum, which is composed of an upper drum 2 and a lower drum 3, where the upper drum 2 is a rotating drum and the lower drum 3 is a fixed drum.

These upper and lower drums 2 and 3 have approximately the same diameter and are disposed one above the other on the same axis, with a gap 4 provided therebetween.

Ha and Hb are a pair of recording and reproducing magnetic heads attached to the upper drum 2 so as to be exposed to the outside within this gap 4, and their angular division is about 1800.

5 is the rotation axis of the upper drum 20.

Reference numeral 6 denotes a pulley for the upper drum 2, which is a driven body, and is integrally attached to the rotating shaft 5.

7 is a motor serving as a rotational drive source; 8 is its rotating shaft;
9 is a pulley attached to the rotating shaft 8.

10 is a belt stretched between these pulleys 6 and 9.

The rotational force of this motor 7 is then applied to the pulley 9-belt 10.
- It is configured to be transmitted through the pulley 6 to the upper drum 2, which is a rotationally driven body.

In the present invention, the rotationally driven body, in this example, the upper drum 2
As the pulley 6, a material having a coefficient of thermal expansion lower than that of the pulley 9 of the rotary drive source, in this example the motor 7, is used.

In this example, the pulley 9 is made of metal such as aluminum, and the pulley 6 is made of plastic such as Delrin.

In this way, for example, when the temperature becomes low, the contraction rate of the pulley 6 of the upper drum 2 is smaller than the contraction rate of the pulley 9 of the motor 7.
Since the shrinkage rate of The decrease in rotational speed due to a decrease in the temperature of the drum 2 is reduced.

In addition, when the temperature rises, the number of revolutions of the upper drum 20 tends to increase, but the number of revolutions decreases compared to when the pulley 6 is made of the same material as the pulley 9.
The increase in 0 rotation speed is reduced.

In this way, changes in the rotational speed of the upper drum 20 due to temperature changes are compensated for, as shown by curve 12 in FIG.

By the way, if both pulleys 6 and 9 are made of aluminum,
When the upper drum 20 rotation speed was 0°C, it was about 0.8% lower than when it was 25°G, but the pulley 6 was Delrin,
When the pulley 9 was made of aluminum, the rotation speed of the upper drum 20 was reduced by only about 0.56% when it was 0°C compared to when it was 25°C.

According to the present invention described above, since the pulley of the rotationally driven body is made of a material having a higher coefficient of thermal expansion than the pulley of the rotational drive source, changes in the rotational speed of the rotationally driven body due to temperature changes are effectively compensated for. .

In the above embodiment, the present invention was applied to a rotating magnetic head device of a VTR, but the present invention is not limited to this. It is particularly suitable for application to a rotational force transmission device that transmits torque to another rotationally driven body via a pulley and a belt.

[Brief explanation of drawings]

FIG. 1 is a schematic front view showing a rotary magnetic head device for a VTR to which the present invention is applied, and FIG. 2 is a characteristic curve diagram for explaining the present invention. 1 is a magnetic tape guide drum, 2 is an upper drum (rotating drum) that is a rotationally driven body, 3 is a lower drum, 6 is a pulley of the upper drum 2, 7 is a motor that is a rotational drive source, 9 is a pulley of motor γ, 10 is a It's a belt.

Claims (1)

[Claims] 1. In a rotational force transmission device configured to transmit rotational force by stretching a belt between a pulley of a rotational drive source and a pulley of a rotationally driven body, the rotational force is transmitted as the pulley of the rotationally driven body. A rotational force transmission device that uses a material with a coefficient of thermal expansion higher than that of a pulley of a drive source to compensate for changes in the rotational speed of the rotationally driven body due to temperature changes.