GB2034420A - Freewheel clutch - Google Patents

Abstract

A clutch, for use in driving an ink-ribbon mechanism in a teleprinter, has an outer drum 1 which is driven and which contains an inner drum 2 connected to the output shaft 4. Rotation of the outer drum in one direction causes the shaft to rotate by virtue of rollers 8 interposed between the interior of the outer drum and wedges 6 attached to the inner drum. Once a given torque is exceeded, the wedges yield against internal springs 7 and the rollers pass over to opposite wedges on the other side. The shaft can now only be driven in the reverse direction and is subject to a similar torque limitation. <IMAGE>

Description

SPECIFICATION Clutch This invention relates to clutches and particularly to mechanical clutches provided with torque-limiting means.

According to the invention in its broadest aspect, there is provided a mechanical clutch arranged to tranmsit motion in either but not both directions of rotation and provided with torque-limiting means operable when a given torque is exceeded in one direction to render the clutch only capable of transmitting motion in the opposite direction.

More specifically the invention provides a mechanical clutch arranged to transmit motion in either but not both directions of rotation and provided with torque-limiting means operable when a given torque is exceeded in one direction to render the clutch only capable of transmitting motion in the opposite direction, the clutch comprising concentrically-arranged driving and driven members, at least one interposer adapted to be wedged between a rigid surface on one member and one side of a double-sided ramp on the other member and resilient means loading the ramp whereby, when the given torque is exceeded, the ramp yields to allow the interposer to pass over the ramp from one side to the other.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which Fig. 1 is a perspective view of the clutch, Fig. 2 is a cross section through the clutch, and Fig. 3 is a part of Fig. 2 showing a stage in operation of the clutch.

Referring firstly to Figs. 1 and 2, the clutch comprises concentrically-arranged driving and driven members in the form, respectively, of an outer drum 1 and inner body 2. The latter has attached to it end plates 3 and a shaft 4. Around the body 2 are arranged pairs of leaf springs 5. Between the pairs of leaf springs are arranged double-sided ramps 6 loaded by rubber springs 7. In the space between the leaf springs, the ramp and the interior rigid surface of the drum 1 are interposers 8 in the form of neddle rollers.

In operation, let it be assumed that the drum 1 is being rotated in an anti-clockwise direction as seen in Fig. 2. The action of the adjacent leaf spring on the roller 8 will be to wedge it between one side of the ramp 6 and the interior surface of the drum 1. This will result in the rotation of the drum 1 being transmitted to the member 2 and the output shaft 4. This will continue only so long as the torque is not sufficient to cause the pressure of the roller 8 on the ramp 6 to overcome the radial force exerted on the latter by the spring 7. Once a predetermined torque is exceeded, the spring 7 will be compressed sufficientlyto allow the ramp to yeild and allow the roller 8 to pass over the peak of the ramp and down the other side. The instant of passing over the peak of the ramp is shown in Fig. 3.Instead of being in a chamber of diminishing width, the roller is now in one of increasing width and the wedging action will cease so that the drive will no longer be transmitted in an anti-clockwise direction.

As soon as the direction of rotation of the drum 1 is reversed, the wedging of the roller will recommence and the shaft 4 will now be driven in the reverse direction until the torque-limiting means acts in the opposite sense.

Thus a drive once started in a given direction will continue to be transmitted in that one direction only until a given torque is exceeded, usually as a result of the driven member being arrested by a stop. For example, the invention could be applied to the reversing mechanism of an ink ribbon drive in a teleprinter or the like.

An advantage of the invention is that the rolling action of the drive means gives a well defined changeover and minimises power loss.

Further advantages are that the driving torque limit may be rapidly varied by merely altering the characteristics of the springs 7, and that a differential torque limit can be achieved by employing different slopes on the two sides of the ramp.

1. A mechanical clutch arranged to transmit motion in either but not both directions of rotation and provided with torque-limiting means operable when a given torque is exceeded in one direction to render the clutch only capable of transmitting motion in the opposite direction.

2. A mechanical clutch arranged to transmit motion in either but not both directions of rotation and provided with torque-limiting means operable when a given torque is exceeded in one direction to render the clutch only capable of transmitting motion in the opposite direction, the clutch comprising concentrically-arranged driving and driven members, at least one interposer adapted to be wedged between a rigid surface on one member and one side of a double-sided ramp on the other member and resilient means loading the ramp whereby, when the given torque is exceeded the ramp yields to allow the interposer to pass over the ramp from one side to the other.

3. A mechanical clutch as claimed in claim 2 in which the interposer is a needle roller.

4. A mechanical clutch as claimed in claim 2 or3 in which the resilient means loading the ramp is a rubber spring which is capable of easy replacement to vary the predetermined value of torque.

5. A mechanical clutch substantially as described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Clutch This invention relates to clutches and particularly to mechanical clutches provided with torque-limiting means. According to the invention in its broadest aspect, there is provided a mechanical clutch arranged to tranmsit motion in either but not both directions of rotation and provided with torque-limiting means operable when a given torque is exceeded in one direction to render the clutch only capable of transmitting motion in the opposite direction. More specifically the invention provides a mechanical clutch arranged to transmit motion in either but not both directions of rotation and provided with torque-limiting means operable when a given torque is exceeded in one direction to render the clutch only capable of transmitting motion in the opposite direction, the clutch comprising concentrically-arranged driving and driven members, at least one interposer adapted to be wedged between a rigid surface on one member and one side of a double-sided ramp on the other member and resilient means loading the ramp whereby, when the given torque is exceeded, the ramp yields to allow the interposer to pass over the ramp from one side to the other. An embodiment of the invention will now be described with reference to the accompanying drawings, in which Fig. 1 is a perspective view of the clutch, Fig. 2 is a cross section through the clutch, and Fig. 3 is a part of Fig. 2 showing a stage in operation of the clutch. Referring firstly to Figs. 1 and 2, the clutch comprises concentrically-arranged driving and driven members in the form, respectively, of an outer drum 1 and inner body 2. The latter has attached to it end plates 3 and a shaft 4. Around the body 2 are arranged pairs of leaf springs 5. Between the pairs of leaf springs are arranged double-sided ramps 6 loaded by rubber springs 7. In the space between the leaf springs, the ramp and the interior rigid surface of the drum 1 are interposers 8 in the form of neddle rollers. In operation, let it be assumed that the drum 1 is being rotated in an anti-clockwise direction as seen in Fig. 2. The action of the adjacent leaf spring on the roller 8 will be to wedge it between one side of the ramp 6 and the interior surface of the drum 1. This will result in the rotation of the drum 1 being transmitted to the member 2 and the output shaft 4. This will continue only so long as the torque is not sufficient to cause the pressure of the roller 8 on the ramp 6 to overcome the radial force exerted on the latter by the spring 7. Once a predetermined torque is exceeded, the spring 7 will be compressed sufficientlyto allow the ramp to yeild and allow the roller 8 to pass over the peak of the ramp and down the other side. The instant of passing over the peak of the ramp is shown in Fig. 3.Instead of being in a chamber of diminishing width, the roller is now in one of increasing width and the wedging action will cease so that the drive will no longer be transmitted in an anti-clockwise direction. As soon as the direction of rotation of the drum 1 is reversed, the wedging of the roller will recommence and the shaft 4 will now be driven in the reverse direction until the torque-limiting means acts in the opposite sense. Thus a drive once started in a given direction will continue to be transmitted in that one direction only until a given torque is exceeded, usually as a result of the driven member being arrested by a stop. For example, the invention could be applied to the reversing mechanism of an ink ribbon drive in a teleprinter or the like. An advantage of the invention is that the rolling action of the drive means gives a well defined changeover and minimises power loss. Further advantages are that the driving torque limit may be rapidly varied by merely altering the characteristics of the springs 7, and that a differential torque limit can be achieved by employing different slopes on the two sides of the ramp. CLAIMS

1. A mechanical clutch arranged to transmit motion in either but not both directions of rotation and provided with torque-limiting means operable when a given torque is exceeded in one direction to render the clutch only capable of transmitting motion in the opposite direction.

2. A mechanical clutch arranged to transmit motion in either but not both directions of rotation and provided with torque-limiting means operable when a given torque is exceeded in one direction to render the clutch only capable of transmitting motion in the opposite direction, the clutch comprising concentrically-arranged driving and driven members, at least one interposer adapted to be wedged between a rigid surface on one member and one side of a double-sided ramp on the other member and resilient means loading the ramp whereby, when the given torque is exceeded the ramp yields to allow the interposer to pass over the ramp from one side to the other.

3. A mechanical clutch as claimed in claim 2 in which the interposer is a needle roller.

4. A mechanical clutch as claimed in claim 2 or3 in which the resilient means loading the ramp is a rubber spring which is capable of easy replacement to vary the predetermined value of torque.

5. A mechanical clutch substantially as described with reference to the accompanying drawings.