GB2614974A

GB2614974A - Linkage assembly for a damper

Info

Publication number: GB2614974A
Application number: GB2302109.0A
Authority: GB
Inventors: Illidge Andrew; Warren Tyler; Kimberley Malcolm
Original assignee: Swegon Air Management Ltd
Current assignee: Swegon Air Management Ltd
Priority date: 2023-02-14
Filing date: 2023-02-14
Publication date: 2023-07-26
Anticipated expiration: 2043-02-14
Also published as: GB2614974B; GB202302109D0

Abstract

A linkage assembly 10 for operating a damper 100 comprises an input member 12 (shaft) for transmitting a rotary movement and a rotary movement output member 18 connectable to a damper blade (120, fig 2). A linkage bar 16 connects the input member to the output member, and wherein rotary movement of the input member translates rotation of the output member through the linkage bar. A connecting part 20 (blade drive bar) connects a first end 30 of the linkage bar to the output member and wherein rotation of the connecting part varies the distance between the first end of the linkage bar and the output member and thereby increases the speed of the rotation of the output member as the distance between the first end of the linkage bar and the output member is reduced. The linkage bar is also connected to the input member by a drive bar 24 rotatably fixed at one of its ends to the linkage bar and fixed at the other of its ends to the input member. Distance variation may be via a cam 26 moveably connected to the linkage bar first end, which is restricted to travel within a cam slot 28.

Description

Linkage Assembly for a Damper

Field of the Invention

The present invention relates to linkages for operating dampers. More specifically, the present invention relates to linkage assemblies for varying operation of damper via an actuator or other input means.

Background

A damper can be used in a duct system to control the flow of air. A damper can open and close accordingly to vary the volume of flow of air through the damper. The duct system can be connected to supply or extract an air flow.

In some operations, the damper is required to move from a fully open to a fully closed position or the reverse. This ensures that the maximum amount of airflow can pass through the damper in the open position, e.g. for venting a room, or that no airflow passes through the damper in the closed position, e.g. for sealing a room. In such operations, there is only the requirement for the control of movement of the damper blade or flap is that it opens or closes. This is often required in a rapid amount of time such as during fires where sealing or venting a room is required quickly. Therefore, the actuation mechanisms which operate the dampers have coarse but fast response times.

There are other situations where the damper blade requires more precise control. In some cases, the damper can be used to provide air ventilation. However, too much ventilation can cause issues with temperature, energy use or dry air. Therefore, the damper blades can be actuated to be positioned at different degrees of opening angles.

Therefore, a damper could be used for air ventilation by controlling the damper blades at the beginning of their opening range to allow a reduced volume of flow compared to the fully open volume of flow.

However, this precise control requires an actuation mechanism having a finer movement range. Whilst this is useful at a nearly-open position, if the damper is required to be rapidly opened or closed, the fine movement is a hindrance for the remainder of the damper blade range.

Furthermore, it can be important to ensure that a damper blade is fully closed (or open) at the extremities of their movement and therefore a high torque can be required to form a seal. However, tolerances and hysteresis can cause difficulties with the precise control of damper blades, particularly at the extremes of their movement ranges.

Therefore, there exists a need to provide precise actuation in particular ranges of movement.

Summary of Invention

In accordance with a first aspect of the invention, there is provided a linkage assembly for operating a damper, the linkage assembly comprising: an input member for transmitting a rotary movement; an output member connectable to a damper blade and having a movement range of rotary motion; a linkage connecting the input member and output member, wherein rotary movement of the input member is translated into rotation of the output member through the linkage; and a connecting part connecting a first end of the linkage to the output member, wherein, rotation of the connecting part varies the distance between the first end of the linkage and the output member such that the speed of the rotation of the output member is increased as the distance between the first end of the linkage and the output member is reduced, and wherein the linkage is connected to the input member by a drive bar rotatably fixed at one of its ends to the linkage and fixed at the other of its ends to the input member.

The rotary movement applied by an actuator device (such as an electric motor) driving or constituting the input member can be constant. Therefore, there are no variations in rotational velocity or torque without any influence. That is to say the power of the input member is constant. Therefore, an input member directly driving a output member (blade drive) would have a constant speed. In the present invention, to vary the speed (rotational velocity) of the output member in only part of the rotation, the linkage between the input member and output member is used. Here, the distance between the first end of the linkage that is the one closest to the output member and the output member is varied. Therefore, the moment of rotation exerted on the output member from the linkage can be increased or reduced compared to the moment of rotation exerted by the input member on the linkage. This difference means that when the first end is moved closer to the output member, the rotation speed of the output member will be faster and, as a consequence, the torque will be lower. Conversely, when the first end is moved further away from the output member, the rotation speed of the output member will be slower and, as a consequence, the torque will be higher. Therefore, the speed of the movement of the output member and thus damper blade can be varied through the rotation of the output member.

The term "slower' refers to speed of rotation of the output member compared to its previous speed of rotation. Therefore, given a previous speed of rotation for the output member for a constant rate of rotation of the input member, the output member has slowed down. Likewise, "faster" refers to an increase in speed of the output member compared to its previous speed for a constant rate of rotation of the input member.

The variation in distance between the first end of the linkage and the output member may also mean that the speed of rotation of the output member can be made faster and/or slower than the speed of rotation of the input member when there is a constant speed of rotation of the input member.

The input member may be a shaft.

The output member may be a shaft. The linkage may comprise a linkage bar. The connecting part may connect a first end of the linkage bar to the output member.

The speed of rotation of the output member may be maximum at the midpoint of its rotation range.

The linkage assembly may comprise an actuator device including the input member or for driving the input member. The actuator device may be, for example, an electric motor, but other actuator devices can be used instead.

Preferably, the varied distance between the first end of the linkage and the output member is measured as the radial distance from the output member. Therefore, the first end of the linkage rotates around the output member and thus rotatably moves the output member as it is connected thereto by the connecting part. Therefore, a rotational movement is translated from the input member to a rotational movement of the output member and it is only the radial distance that is varied. This provides a simpler mechanism than providing different directional movements.

Preferably, the output member is rotatable through at least or at most substantially a quarter of a revolution. More preferably, the output member is rotatable to move a damper blade between an open and a closed position for controlling airflow through a passage. A damper blade moves between a closed position, where the blade can be considered to be at 0 degrees and perpendicular to the passage, to 90 degrees where the blade can be considered to be parallel to the passage. Therefore, an output member directly connected to the damper blade requires the same range of motion. The output member may be capable to move slightly further than the closed position so that there is tolerance to ensure that the damper blade can seal in a closed position and move to a fully open position.

Preferably, the speed of the rotation of the output member is slower, the same and faster than rotary movement of the input member throughout the movement range of the output member. The rotational speed of the output member is varied through its rotation. Therefore, it can start rotation at the same speed as the input member, speed up through a middle range and then slow down to be slower than the input member at the end of its range. The input member can have more or less or the same rotational movement than the output member. For instance, the input member can move through 120 degrees to translate into 90 degrees of movement for the output member. Therefore, the rotation of the output member would need to be slower in comparison to the input member over the total range. This can result in the output member speed being varied throughout the movement range. The opposite is also possible for an input member with less movement.

Preferably, the speed of rotation of the output member is slower near at least one, preferably both, of the extremities of its movement range for a given constant input member rotary speed. Consistent with what was described previously, the speed of rotation of the rotatable blade is compared to the speed of rotation of the rotatable blade at another point in its movement range, or is compared to the speed of rotation of the input member. Therefore, for example, given a previous speed of rotation for the output member for a constant rate of rotation of the input member, the output member has slowed down. The slower speed at the extremes, i.e. one or both of the closed and open position of the blades allows for more precise control in this area for the same input member movement. Therefore, the output member has a comparatively faster speed at the midrange of movement.

In the present invention, the linkage or linkage bar is connected to the input member by a drive bar rotatably fixed at one of its ends to the linkage or linkage bar and fixed at the other of its ends to the input member. Therefore, for a given equal distance from the input member to a second end of the linkage or linkage bar to the output member from the first end of the linkage or linkage bar, the movement of the linkage or linkage bar is relatively linear. If this distance were maintained, the translation of the movement of the input member to the output member would be 1:1.

Preferably, the variation of the distance between the first end of the linkage and the output member is by a cam. More preferably, the linkage assembly comprises a cam slot for variation of the distance between the first end of the linkage and the output member, wherein the first end of the linkage is restricted to travel within the cam slot. A cam can be shaped to provide a variation in the distance throughout the drive blade range. Therefore, a simpler manufacturing process is provided. A cam slot prevents the linkage from detaching and provides a consistent movement action.

Preferably, the connecting part comprises a blade drive bar connecting the output member to the first end of the linkage, the blade drive bar preferably comprising a drive slot, wherein the first end of the linkage is restricted to travel in the drive slot. The drive slot is a radial angled slot from the blade drive bar. Therefore, the first end of the linkage is restricted in its movement to only move in a radial direction through the drive slot (as dictated by the cam). This ensures a smooth movement.

Preferably, the torque of the rotation of the output member is increased as the distance between the first end of the linkage and the output member is increased. Therefore, a greater torque can ensure that a damper blade is fully engaged against any seals, such as in a closed position. Consistent with what was described previously, the torque of the rotation of the rotatable blade is compared to the torque of the rotation of the rotatable blade at another point in its movement range, or is compared to the torque of rotation of the input member.

In a second aspect of the invention, there is provided a damper comprising: a passage; at least one damper blade arranged in the passage and moveable between open and closed positions for controlling an airflow through the passage; a linkage assembly for operating the damper, the linkage assembly comprising: an input member for transmitting a rotary movement; a output member fixedly connected to the at least one damper blade and having a movement range of rotary motion; a linkage connecting the input member and output member, wherein rotary movement of the input member is translated into rotation of the output member through the linkage; and a connecting part connecting a first end of the linkage to the output member, wherein, rotation of the connecting part varies the distance between the first end of the linkage and the output member such that the speed of the rotation of the output member and connected damper blade is increased as the distance between the first end of the linkage and the output member is reduced, and wherein the linkage is connected to the input member by a drive bar rotatably fixed at one of its ends to the linkage and fixed at the other of its ends to the input member. Therefore, the speed of rotation of the blade is varied through its range to provide precise control where it is required, such as during points to control airflow.

Preferably, the movement range of the damper blade is slowest near the closed and/or open positions for a given constant input member rotary speed. The slightly open position of a blade can be important as it is at this point where a small amount of airflow is required. Therefore, by having the slowest speed at the nearly closed and/or nearly open regions, the operation of the input member will result in a smaller movement of the blade providing more precise control.

Preferably, the nearly closed region is between 0 degrees and 10 degrees of operation.

More preferably, it is between 0 degrees and 20 degrees of operation. The 0 degrees is the fully closed position for the blade, where the blade is positioned perpendicular to the airflow through the passage, such that is blocks the airflow. Therefore, the precise operation of the blade is at the nearly closed region.

Preferably, the varied distance between the first end of the linkage and the output member connected to the damper blade is measured as the radial distance from the output member.

Preferably, the damper blade is rotatable through substantially a quarter of a revolution between closed and open positions. The damper blade moves between a closed position where it blocks air flow, to an open position where it does not block air flow. In this regard, the damper blade can rotate between a vertically aligned position where the face of the blade is facing the air flow (perpendicular), to a horizontally aligned position where the face of the blade is inline with the flow of air. In the closed position if there is more than one blade, each blade and its adjacent blade can form a wall of vertically aligned blades. As there is no gap between the blades, the air flow can be stopped or greatly reduced in this position.

Preferably, the speed of rotation of the damper blade is slower near the fully open or fully closed positions for a given constant input member rotary speed.

The damper may comprise an actuator device including the input member or for driving the input member. The actuator device may be, for example, an electric motor, but other actuator devices can be used instead.

The preferable features of the first aspect of the invention are equally applicable to the second aspect of the invention, and vice versa.

Brief Description of the Figures

Figure 1 shows an isometric view schematic of a damper and linkage assembly according to the present invention; Figure 2 shows a side sectional view schematic of the damper of Figure 1; Figure 3 shows a front view schematic of the damper and linkage assembly of Figure 1; Figure 4 shows an isometric view schematic of the damper and linkage assembly of Figure 1 with the linkage assembly open; Figure 5 shows a side view schematic of the open linkage assembly of Figure 4; and Figure 6 shows a side view render of the same side view of the linkage assembly as Figure 5.

A fully and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification. Reference now will be made in detail to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention.

It will be apparent to those of ordinary skill in the art that various modifications and variations can be made in the present invention without departing from the scope of the invention. For instance, features described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents.

Other objects, features, and aspects of the present invention are disclosed in the remainder of the specification. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions.

A listing of reference symbols used herein is given at the end of the description. Repeat use of reference symbols in the present specification and drawings is intended to represent the same or analogous features or elements.

Referring to Figure 1, there is provided a damper 100 and linkage assembly 10 in accordance with an embodiment. The damper 100 is formed of an elongate cylindrical passage 102 and has a first end 104 and a second end 106. The damper 100 is formed to allow an air flow through the passage 102 wherein the first damper end 104 and second damper end 106 form an inlet and outlet depending on the direction of flow of air.

The passage 102 can be formed as any air passageway such as a duct or as a chimney and can be of any shape to allow air flow there through, for instance square passages 102 can be used.

Referring to Figure 2, the sectional view shows the inside of the damper 100. The damper has a hollow body forming the passage 102. Therefore, the first and second ends 104, 106 allow an airflow through the passage 102. A damper blade 120 is positioned in the passage 102. The damper blade 120 is a plate shaped to fill the mouth of the passage 102 in one orientation and is moveable to a second orientation whereby the mouth of the passage 102 is not filled. When the damper blade 120 fills the passage 102, the blade is in a closed position (as shown in Figure 2) and prevents an air flow through the passage 102 by blocking the passage 102. Therefore, in the closed position the blade 120 is positioned across the passage 102 such that the face of the plate shaped blade 120 faces the air flow through the passage 102.

In an open position, the blade 120 is orientated such that air flow can pass through the passage 102. This is achieved by rotating the blade 102 through an axis following its line of diameter (radial line). When the blade 120 is rotated approximately 90 degrees from its closed position, the surface of the plate of the blade 120 will be in-line with the air flow through the passage 102 between the first and second ends 104, 106.

The blade 120 can also be orientated in any position between the open and closed positions.

Whilst a circular blade 120 or a short cylindrical blade 120 has been described, the blade can be any shape that is suitable to fill the passage 102. For instance, the blade 120 can be square or rectangular for a square or rectangular passage 102. In such a case, the rotation axis of the blade 120 can be a line bisecting the blade 120. The blade 120 also does not need to be a single blade 120 but can be multiple blades 120. In such a situation, the passage 102 can be closed by the blades overlapping to form a wall, i.e. an effective single plate.

To move the damper blade 120, a means of rotation is used. A linkage assembly 10 is positioned on the outside of the damper 100. The linkage assembly includes an input member in the form of a rotatable shaft 12 which provides a rotational force. The rotatable shaft 12 is inserted into an actuator device which in this embodiment is an electric actuator (the rest of which is not shown) but the actuator device may take other forms. The rotation force from the rotatable shaft 12 is used to rotate the damper blade 120 between open and closed positions. Whilst a rotatable shaft 12 can be positioned in direct contact with a damper blade 120 such that rotation of the actuator shaft directly rotates the damper blade 120, a linkage assembly 10 can be provided by which the actuator shaft and damper blade are not in direct contact.

The linkage assembly 10 has an actuator cover 14 to enclose the internal mechanism of the linkage assembly 10.

Referring to Figure 3, the damper blade 120 in the closed position closes the passage 102, as can be seen from a front direction through the passage 102. A damper seal 108 surrounds the damper blade 120 to ensure that in the closed position air flow can be prevented from passing through the passage 102. The seal 108 allows the blade 120 to move freely between the open and closed positions whilst maintaining a clearance between the damper walls and the blade edges without compromising the sealing.

In Figure 3, it can also be seen that the rotatable shaft 12 is positioned along a radial line of the damper blade. Therefore, the axis of rotation for the blade 120 extends through the rotatable shaft 12. However, as discussed below, in the present embodiment, it is not the rotatable shaft 12 that is in direct rotational contact with the blade 120.

Referring to Figure 4, an isometric view of the damper 100 shown similar to that of Figure 1. However, the assembly cover 14 is removed from the linkage assembly 10 to provide a view thereunder. In operation an assembly cover 14 can be provided to ensure that moving parts are enclosed and to protect from foreign objects interfering with the mechanism.

In the linkage assembly 10 there is provided a output member or rotatable blade drive 18. The output member 18 is a rotatable fastener such as a pin or shaft that is at least partly positioned outside the passage 102. The output member 18 is connected to the damper blade 120 inside the passage 102. Therefore, rotation of the output member 18 from the linkage assembly 10 side will result in the rotation of the damper blade 120 in the passage 102. Therefore, the output member 18 can be directly fixed to the damper blade 120 such that it is a direct rotational translation of movement.

The rotatable shaft 12 is connected to the output member 18 by a linkage bar 16 that translates a rotational movement from the rotatable shaft 12 into a rotational movement of the output member 18. The linkage bar 16 is an elongate bar having a pin, dowel or divot at its ends to allow a rotational connection to further parts, such that the linkage bar 16 can be rotatable connected to further parts at its ends. The movement of the output member 18 is provided by a connecting part that connects the output member 18 to the linkage bar 16. The rotation of the rotatable shaft 12 is not a direct 1:1 relationship with the rotation of the output member 18 by virtue of the connecting part. Instead, the torque and velocity is varied throughout the range of the output member 18 and hence the damper blade 120 as it moves between open and closed positions.

The linkage bar 16 can also be referred to as a drive linkage.

Whilst a linkage bar 16 is described, there are various means for translation of the rotational movement, such as gearing, chains or springs. Likewise, the movement of the actuator device can be in directions other than rotational, such as linear displacement actuators.

Referring to Figure 5, a side view of damper 100 and linkage assembly 10 with the assembly cover 14 removed to further describe the connecting part and associated features.

The rotatable shaft 12 is connected to the linkage bar 16 by a drive bar 24. The drive bar 24 is fixed at one end to the rotatable shaft 12 such that rotation of the rotatable shaft 12 causes the rotation of the drive bar 24. As these parts are fixed directly, the movement is a direct translation of rotational movement. The drive bar 24 is an elongate part that is rotatably connected at its other end to the linkage bar 16. The connection to the linkage bar 16 is at the second end 32 of the linkage bar 16 and is connected by a pin or similar as described above. Therefore, movement of the rotatable shaft 12 rotates the drive bar 24 which pushes or pulls the linkage bar 16 relative to the drive bar 24 depending on the direction of rotation of the rotatable shaft 12.

Similarly to the drive bar 24, a blade drive bar 20 is fixed to the output member 18 such that rotation of the blade drive bar 20 causes rotation of the output member 18 (or vice versa). As these parts are fixed directly, the movement is a direct translation of rotational movement. The blade drive bar 20 is an elongate body that is connected at its one end to the output member 18. The blade drive bar 20 is also connected to the linkage bar 16.

However, unlike the drive bar 24, the blade drive bar 20 has a blade drive slot 22 extending from one end to another end, i.e. toward the connection with the output member 18. A first end 30 of the linkage bar 16 is slidably connected to the blade drive slot 22 using a pin or rivet such that the first end 30 can slide within the slot 22. The first end 30 can also rotate within the blade drive slot 22. Therefore, movement of the linkage bar 16 (such as from the rotatable shaft 12) will cause some rotational force on the output member 18 via the blade drive bar 20 and some movement of the first end 30 of the linkage bar 16 within the blade drive slot 22.

Within the linkage assembly 10, there is also provided a surface cam 26. The surface cam 26 is also movably connected to the first end 30 of the linkage bar 16. The surface cam 26 is positioned near to the output member 18 such that the movement of the linkage bar 16 is constrained by the first end 30 and: the rotation of the blade drive bar 20 that is connected to the output member 18; the sliding within the slot 22 of the blade drive bar 20, and the position of the surface cam 26.

The surface cam 26 is positioned such that the distance between the first end 30 and the output member 18 varies as the first end 30 is rotated around the output member 18. Therefore, the radial distance is changed as the surface cam constrains the first end 30 to slide to a particular position in the blade drive slot 22 as the blade drive bar 20 is rotated.

The rotatable shaft 12 and associated drive bar 24 has a fixed distance to the second end 32 of the linkage bar 16. Therefore, the radial distance between the rotatable shaft 12 and the second end 32 does not change through the rotation of the drive bar 24.

The variation of the distance of the output member 18 and the first end 30 of the linkage bar 16 means that for a given rotation of the rotatable shaft 12, the output member 18 can rotate faster (more speed) than the rotatable shaft 12 when the distance between the output member 18 and the first end 30 is less than the distance between the rotatable shaft 12 and the second end 32. For a given power of actuator device, this means that the torque is lower when the speed is faster for the output member 18.

The variation of the distance of the output member 18 and the first end 30 of the linkage bar 16 also means that for a given rotation of the rotatable shaft 12, the output member 18 can rotate slower (less speed) than the rotatable shaft 12 when the distance between the output member 18 and the first end 30 is more than the distance between the rotatable shaft 12 and the second end 32. For a given power of actuator device, this means that the torque is higher when the speed is slower for the output member 18.

Therefore, the speed and torque for output member 18, and thus damper blade 120, can vary through its range for a given linear operation and rotation of a rotatable shaft 12.

The second end 32 can also be referred to as a cam follower as it follows the surface cam 26 The surface cam 26 has a cam slot 28 where the pin or rivet, etc. of the first end 30 slides through. The cam slot 28 has a curved shape to ensure a smooth movement of the first end 30 through its movement. The cam slot 28 is a partial top half of a circle, i.e. an arch, where the start of the cam slot 28 is at the furthest distance from the output member 18, the middle (apex) of the cam slot 28 is the closest to the output member 18 and the end of the cam slot 28 is again at the furthest distance from the output member 18. The start and end of the cam slot 28 are the open and closed positions of the damper blade 120 as it moves from one position to the other. Where the distance between the cam slot 28 and the output member 18 are at their greatest, the movement of the output member will be comparatively low speed and high torque compared to when the distance between the cam slot 28 and the output member 18 are at their least. This can also be compared to the rotatable shaft 12 which will have a constant speed and torque. Therefore, the damper blade 120 moves slowest at the opening and closing positions and speeds up to its highest speed and lowest torque at the position between the opened and closed positions.

This allows the output member 18 and thus damper blade 120 to be controlled at its highest precision near the fully open and fully closed positions. Therefore, the movement of the rotatable shaft 12 will translate into the smallest movement of the output member 18 and thus damper blade 120 for all of its movement.

Whilst an arch has been described for the cam slot 28, other shapes can be used to vary the speed and torque as required. For instance, the fully open position can also be high speed and low torque as precision may not be required in this range.

Referring to Figure 6, the same damper 100 side view of Figure 5 is shown. Here the solid lines between the rotatable shaft 12, the first end 30, the second end 32 and the output member 18 show fixed distances between these. Importantly, the Input Member to Output Member Distance 38 does not vary and is a fixed distance. Likewise the First End to Second End Distance 34 and the Input Member to Second End Distance 36 is fixed. Therefore, for a given rotation of the rotatable shaft 12, there is a known movement of the second end 32 of the linkage bar and a limited movement for the first end 30. The Output Member to First End Distance 40 can vary, such that the first end 30 moves toward or away from the output member 18. It is this variation in radial distance and thus angular moment of force that provides the variable speed and torque for a given linear drive actuator 12 for precise control of a output member 18 at given parts of its movement.

Reference Signs -Linkage Assembly 12-Rotatable Shaft 14 -Assembly Cover 16 -Linkage Bar 18-Output Member 20-Blade Drive Bar 22 -Blade Drive Slot 24-Drive Bar 26 -Surface Cam 28-Cam Slot 30-Cam Follower / First End 32-Second End 34 -First End to Second End Distance 36-Input Member to Second End Distance 38-Input Member to Output Member Distance 40 -Output Member to First End Distance 100-Damper 102-Passage 104-First Damper End 106-Second Damper End 108-Damper Seals 120-Damper Blade

Claims

CLAIMS: 1. A linkage assembly for operating a damper, the linkage assembly comprising: an input member for transmitting a rotary movement; an output member connectable to a damper blade and having a movement range of rotary motion; a linkage connecting the input member and output member, wherein rotary movement of the input member is translated into rotation of the output member through the linkage; and a connecting part connecting a first end of the linkage to the output member, wherein, rotation of the connecting part varies the distance between the first end of the linkage and the output member such that the speed of the rotation of the output member is increased as the distance between the first end of the linkage and the output member is reduced, and wherein the linkage is connected to the input member by a drive bar rotatably fixed at one of its ends to the linkage and fixed at the other of its ends to the input member.
2. The linkage assembly according to claim 1, wherein the linkage comprises a linkage bar.
3. The linkage assembly according to any preceding claim, wherein the speed of rotation of the output member is maximum at the midpoint of its rotation range.
4. The linkage assembly according to any preceding claim, wherein the varied distance between the first end of the linkage and the output member is measured radially from the output member.
The linkage assembly according to any preceding claim, wherein the output member is rotatable through at least or at most substantially a quarter of a revolution.
6. The linkage assembly according to any preceding claim, wherein the output member is rotatable to move a damper blade between an open and a closed position for controlling airflow through a duct.
7. The linkage assembly according to any preceding claim, wherein the speed of rotation of the output member is slower near at least one of the extremities of its movement range for a given constant input member rotary speed.
8. The linkage assembly according to any preceding claim, wherein the variation of the distance between the first end of the linkage and the output member is by a cam.
9. The linkage assembly according to any preceding claim, comprising a cam slot for variation of the distance between the first end of the linkage and the output member, wherein the first end of the linkage is restricted to travel within the cam slot.
10. The linkage assembly according to any preceding claim, wherein the connecting part comprises a blade drive bar connecting the output member to the first end of the linkage, the blade drive bar comprising a drive slot, wherein the first end of the linkage is restricted to travel in the drive slot.
11. The linkage assembly according to any preceding claim, wherein torque of the rotation of the output member is increased as the distance between the first end of the linkage and the output member is increased.
12. A damper comprising: a passage; at least one damper blade arranged in the passage and moveable between open and closed positions for controlling an airflow through the passage; a linkage assembly for operating the damper, the linkage assembly comprising: an input member for transmitting a rotary movement; an output member fixedly connected to the at least one damper blade and having a movement range of rotary motion; a linkage connecting the input member and output member, wherein rotary movement of the input member is translated into rotation of the output member through the linkage; and a connecting part connecting a first end of the linkage to the output member, wherein, rotation of the connecting part varies the distance between the first end of the linkage and the output member such that the speed of the rotation of the output member and connected damper blade is increased as the distance between the first end of the linkage and the output member is reduced, and wherein the linkage is connected to the input member by a drive bar rotatably fixed at one of its ends to the linkage and fixed at the other of its ends to the input member.
13. The damper according to claim 12, wherein the movement range of the damper blade is slowest near the closed and/or open positions for a given constant input member rotary speed.