GB1578438A

GB1578438A - Shaft rotation actuators

Info

Publication number: GB1578438A
Application number: GB4849976A
Authority: GB
Original assignee: LOVEGROVE A
Current assignee: LOVEGROVE A
Priority date: 1978-02-17
Filing date: 1978-02-17
Publication date: 1980-11-05

Description

(54) IMPROVEMENTS RELATING TO SHAFT ROTATION ACTUATORS (71) I, ALAN MARTIN LOVEGROVE, of Rivendell, 6 The Deans Quarry, Burleigh Lane, Brimscombe, Gloucestershire, a British Subject, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with actuators for imparting variable torque to a rotatable shaft.

With many types of equipment which employ an opening function the initial effort required is often considerably greater than the effort needed for the subsequent stages of the opening movement. This applies, for instance, to inlet vane dampers for use in conjunction with a fan where the vanes are opened in concert by a rotating member. A pressurized air flow impinging on the vanes tends to hold them firmly in the closed position so that a high initial torque is needed to open the damper but thereafter a much lower torque is sufficient to complete the opening operation. If a constant torque is applied then once the initial stage of opening is completed the final opening movement will be comparatively rapid so that there is a danger that damage could occur to the equipment or, where the degree of opening of the damper depends upon other parameters oscillations could set up due to hunting of the devices controlling opening of the damper.

Accordingly, this invention provides an actuator for rotating a shaft which will be connected to a member having a high initial torque resistance but progressively lower torque resistance upon rotation from the initial position, the actuator comprising an operating member and a linkage having first and second arms which are pivotally interlinked, the first arm being pivotally connected at its free end to the operating member, and the second arm being fixed at its free end to the shaft, and the operating member is constructed to move the free end of the first arm in a substantially linear direction which is substantially parallel to the position of the second arm when the shaft is in the initial position and substan tially normal to the position of the first arm when the shaft is in the initial position.

The relationship of the first and second arms and the direction of movement of the operating member are such that, as the shaft is rotated from the initial position the torque available is many times greater over the initial few degrees of rotation of the shaft than it is for the remaining period of rotation of the shaft under control of the actuator. Thus substantial effort is applied to the shaft initially which will overcome the high initial torque resistance but, thereafter, a much lower, and substantially constant torque will be applied to the shaft for the remaining period of rotation of the shaft.

This therefor substantially alleviates the problems discussed above in relation to inlet vane dampers, for instance.

In the preferred embodiment the operating member comprises a bar or rod extending in the direction of movement of the free end of the first arm. Generally this rod or bar will be caused to follow a linear path when performing the operating function but clearly the device will operate satisfactorily (although with somewhat modified characteristics) if the bar or rod is caused to move along a path which varies to some extent from a direct linear path. For instance the end of the bar remote from the point of connection of the first arm may be connected to an eccentric drive member. It is preferred that the bar or rod should be guided by one or more guide rollers and it is particularly advantageous to provide that one of the guide rollers is mounted co axially with the shaft, since then a possible bending moment exerted on the shaft will be counteracted by an opposite moment applied by the bar or rod to the guide roller which is co-axially mounted on the shaft.

For ease of construction it is advantageous to provide that the free end of the first arm is pivotally connected to a connecting member attached to the bar or rod. Ideally the position of the connecting member with respect to the bar or rod is adjustable in the direction of movement of the free end of the first arm to alter the attitude of the first arm by a few degrees. This enables the relative positions of the parts of the actuator to be varied on installation of the actuator and also to modify slightly the operational characteristics of the actuator, particularly in respect of the first few degrees of rotation of the shaft from the initial position. For similar reasons it is desirable to provide that the fixed position of the free end of the second arm is adjustable about the shaft.

The maximum torque enhancement effect for movement of the shaft from the initial position is achieved if the direction of movement of the operating member is parallel to the second arm and normal to the first arm when the shaft is in the initial position.

However, some tolerance either way will generally be acceptable although preferably this will not exceed 15 in either case.

Obviously increase in variation of the parallel and normal conditions of the first and second arms will lower the benefit achieved, but this may be desired or acceptable in certain situations.

In most cases it will be preferred that the first and second arms should be of substantially equal length but increase in length of the second arm with respect to the first arm will cause the torque characteristics to approach closer to a linear effect whilst increase in length of the first arm with respect to the second arm will increase the initial angle of rotation of the shaft during which the substantially high torque will be applied.

Generally the operating member will be effective to move the shaft through a quarter of a revolution, although for certain applications smaller or larger rotation angles may be desirable.

The shaft of the actuator may, for instance, comprise the operational member of an inlet vane damper or a butterfly valve for a fluid supply system. Where an inlet vane damper associated with a fan of a gas flow system is involved then the main requirement is to provide an initial high torque to force the vanes open against the pressurized air flow impinging thereon. After this the resistance to rotation of the vanes is considerably lower. When the actuator is used with a butterfly valve, however, then the volume of fluid passed with respect to the extent of movement of the operating member becomes much closer to linear than compared with the situation where the shaft attached to the butterfly valve is subjected to a uniform rotation.

The invention may be performed in various ways and a preferred embodiment thereof will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a variable torque actuator of this invention Figure 2 is a diagrammatic representation of the operation of the actuator of Figure 1; Figure 3 is a view in the direction of the arrow III of Figure 1; Figure 4 is a cross-section on line IV of Figure 1; and Figures 5 and 6 illustrate adjustments to the relative positions of the parts of the actuator which may be performed.

The device shown in Figure 1 converts a linearly applied force to a rotationally applied force for rotating a shaft 1 which may control, for isntance, the opening of an inlet vane damper. The linearly applied force acts on an actuator rod 2 which is caused to move in the direction of the arrow 3. When the shaft is in the position where the damper is closed an arm 4 secured to the shaft 1 lies parallel with the rod 2. The other end of the arm 4 is mounted to a second arm 5 via a pivot 6 and the other end of the arm 5 is itself pivotally attached at 7 to a connecting member 8 secured to the rod 2.

Figure 2 shows four stages of movement of the arms 4 and 5 relative to four equal movement steps of the rod 2. Before an actuating force is applied to the apparatus the two pivots 6 and 7 are in the position shown in Figure 1, and after the first stage of the movement they will have moved to the position Al, Bl resulting in an angular displacement of the arm 4 of about 3q0.

After the next stage of linear movement of the rod 2 the pivots will attain the position A2, B2 resulting in an additional angular displacement of the arm 4 of about 16120.

Further stages of movement to the positions A3, B3 and A4, B4 result in additional angular displacements of the arm 4 of about 220 and 25 respectively.

Thus it will readily be seen that for a constant actuating force the initial torque applied to the shaft 1 is much greater than that applied during later stages of movement, where the torque applied is lower and fairly constant.

As can be seen, particularly from Figure 3, the arm 4 is a U-shaped member whose free ends receive the pivot 6 for the arm 5.

A slot 9 is cut out of the other end of the arm 4 and is enlarged at the position where it receives the shaft 1. A bolt 10 urges the parts of the arm 4 either side of the slot 9 towards one another so as to clamp the arm tightly about the shaft 1. The relative positions of the shaft 1 and the arm 4 may be varied by slackening the bolt 10, rotating the arm 4 to the required position and then securing the bolt 10 again. It will be seen that the shaft 1 also carries a roller 11 co-axially therewith and the actuator rod bears on this roller (and one or more further rollers along its direction of movement if necessary). The actuator rod 2 in contact with the roller 11 prevents the imparting of a bending moment to the shaft 1.

The securing of the connecting member 8 to the actuator rod 2 is illustrated particularly with reference to Figure 4. The connecting member 8 again comprises a U-shaped member whose free ends receive the pivot 7 for the arm 5. The other end of the connecting member 8 is clamped in position by a bolt 12 which passes through a hole in an angled support 13 welded to the actuator rod 2. If the bolt 12 is slackened off then the position of the connecting member 8 relative to the actuator rod may be varied as illustrated in Figure 5, the bolt 12 then being clamped in the required new position. From Figure 5 it will be appreciated that, by this means, the position of the arm 5 may be varied within wide limits without substantially affecting the initial position of the shaft 1. As shown in Figure 6 it is also possible, by this means, to adjust the final position of operation of the actuator (so that the arm 4 moves to a new position between the dashed lines 14) without substantially affecting the initial position of the shaft (i.e. the position illustrated in Figure 1).

WHEAT I CLAIM IS:- 1. An actuator for rotating a shaft which will be connected to a member having a high initial torque resistance but progressively lower torque resistance upon rotation from the initial position, the actuator comprising an operating member and a linkage having first and second arms which are pivotally interlinked, the first arm being pivotally connected at its free end to the operating member, and the second arm being fixed at its free end to the shaft, and the operating member is constructed to move the free end of the first arm in a substantially linear direction which is substantially parallel to the position of the second arm when the shaft is in the initial position and substantially normal to the position of the first arm when the shaft is in the initial position.

position.

2. An actuator according to claim 1, wherein the operating member comprises a bar or rod extending in the direction of movement of the free end of the first arm.

3. An actuator according to claim 2, wherein the bar or rod is guided by one or more guide rollers.

4. An actuator according to claim 3, wherein one of the guide rollers is mounted co-axially with the shaft.

5. 2 An actuator according to any one of claims 2 to 4, wherein the free end of the first arm is pivotally connected to a connecting member attached to the bar or rod.

6. An actuator according to claim 5, wherein the position of the connecting member with respect to the bar or rod is adjustable in the direction of movement of the free end of the first arm to alter the attitude of the second arm by a few degrees.

7. An actuator according to any one of claims 1 to 6, wherein the fixed position of the free end of the second arm may be adjusted about the shaft.

8. An actuator according to any one of claims 1 to 7, wherein the operating mem ber is effective to move the shaft through a quarter of a revolution.

9. An actuator according to any one of claims 1 to 8, wherein the first and second arms are substantially equal in length.

10. An actuator according to any of claims 1 to 9, wherein the shaft is the operational member of an inlet vane damper for a fluid supply system.

11. An actuator according to any one of claims 1 to 9, wherein the shaft is the operational member of a butterfly valve for a fluid supply system.

12. An actuator substantially as herein described with reference to the accompany- ing drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. arm tightly about the shaft 1. The relative positions of the shaft 1 and the arm 4 may be varied by slackening the bolt 10, rotating the arm 4 to the required position and then securing the bolt 10 again. It will be seen that the shaft 1 also carries a roller 11 co-axially therewith and the actuator rod bears on this roller (and one or more further rollers along its direction of movement if necessary). The actuator rod 2 in contact with the roller 11 prevents the imparting of a bending moment to the shaft 1. The securing of the connecting member 8 to the actuator rod 2 is illustrated particularly with reference to Figure 4. The connecting member 8 again comprises a U-shaped member whose free ends receive the pivot 7 for the arm 5. The other end of the connecting member 8 is clamped in position by a bolt 12 which passes through a hole in an angled support 13 welded to the actuator rod 2. If the bolt 12 is slackened off then the position of the connecting member 8 relative to the actuator rod may be varied as illustrated in Figure 5, the bolt 12 then being clamped in the required new position. From Figure 5 it will be appreciated that, by this means, the position of the arm 5 may be varied within wide limits without substantially affecting the initial position of the shaft 1. As shown in Figure 6 it is also possible, by this means, to adjust the final position of operation of the actuator (so that the arm 4 moves to a new position between the dashed lines 14) without substantially affecting the initial position of the shaft (i.e. the position illustrated in Figure 1). WHEAT I CLAIM IS:-

1. An actuator for rotating a shaft which will be connected to a member having a high initial torque resistance but progressively lower torque resistance upon rotation from the initial position, the actuator comprising an operating member and a linkage having first and second arms which are pivotally interlinked, the first arm being pivotally connected at its free end to the operating member, and the second arm being fixed at its free end to the shaft, and the operating member is constructed to move the free end of the first arm in a substantially linear direction which is substantially parallel to the position of the second arm when the shaft is in the initial position and substantially normal to the position of the first arm when the shaft is in the initial position.

position.