A Mechanism for Opening and Closing a Barrier

This invention relates to a mechanism for opening and closing a barrier such as a gate.

Gates are commonly used in fence lines or farmyards to allow access and to secure vehicles, property or livestock.

However, for a vehicle to pass through the gate the driver has to vacate the vehicle to open the gate and then return it to the closed position once the vehicle has been driven through the gate. The opening and closing of gates can thus become time consuming.

Conventional gate opening mechanisms make use of electric motors in order to drive the opening and closing of the gate. Such mechanisms consume power and require connection to a power source upon installation, which can be problematic when the gate is to be installed a distance from the nearest premises or power lines. In addition, conventional powered gate mechanisms resist manual operation and thus inhibit use by pedestrians.

The present invention seeks to provide an improved mechanism for opening and closing a barrier.

Accordingly, the present invention provides a mechanism for opening and closing a barrier, comprising: a first, elongate support member for supporting said barrier for pivotal movement between a closed and an open position; a second, barrier support member mounted for pivotable movement about said first support member between said closed and open positions; a first, opening drive mechanism operable for moving said barrier support member from said closed position to said open position under the action of gravity; a second, closing drive mechanism actuable to move said barrier support member from said open

position to said closed position under the action of gravity; and a control mechanism for actuating said second, closing drive mechanism.

In a preferred form of the invention said opening drive mechanism comprises first cooperating means on said first and second support members arranged such that when said barrier support member is in said closed position said first cooperating means urges said barrier support member to pivot from said closed position to said open position under weight of said barrier.

Advantageously, said first cooperating means comprises: first and second vertically spaced cam means on said first and second support members, said cam means having respective, opposing upper and lower cam surfaces engageable with one another; and wherein said opposing cam surfaces are shaped such that when said barrier support member is in said closed position the weight of said barrier urges said upper cam surface to ride over said lower cam surface thereby to pivot said barrier support member from said closed position to said open position.

Preferably, said closing mechanism comprises: a drive member; and second cooperating means on said second, barrier support member and said drive member arranged such that when said second, barrier support member is in said open position actuation of said control mechanism causes the cooperating means on said drive member to engage said cooperating means on said second, barrier support member to pivot said second, barrier support member from said open position to said closed position under the weight of said barrier.

Advantageously, said second cooperating means comprises: said second cam means on said second, barrier support member and a third cam means on said drive member, said third cam means having an upper cam surface engageable with said lower cam surface of said second cam means; wherein said drive member is moveable vertically in response to actuation of said control mechanism to cause said third cam surface to engage said lower cam surface of

said second cam means; and wherein said cam surfaces are shaped such that when said barrier support member is in said open position, the weight of said barrier urges said upper cam surface to ride over said lower cam surface thereby to pivot said barrier support member from said open position to said closed position.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a front elevation of a barrier, having a mechanism for opening and closing in accordance with a preferred form of the invention;

Figure 2 is a vertical section through the lower portion of a support for the barrier of the Figure 1;

Figure 3 is a vertical section through the upper end portion of the support of figure 2;

Figure 4 is a partial section through a latch mechanism for the barrier of Figure 1 ;

Figure 5 is a plan view of a treadle of the opening and closing mechanism;

Figure 6 is a side elevation of the treadle of Figure 5 in a retracted attitude;

Figure 7 is a plan view, partially in section, of a part of the control mechanism for the opening and closing mechanism, with the barrier closed;

Figure 8 is a perspective view of the mechanism of Figure 7 with the barrier open;

Figure 9 is a perspective, sectional view of the mechanism of Figure 8, along the line 8-8 in Figure 8;

Figure 10 is a view similar to that of Figure 2, of a second embodiment according to the present invention;

Figure 11 is a plan view of part of a control mechanism for the embodiment of Figure 10;

Figure 12 is a perspective view of the lower part of the support of the embodiment of Figures 10 and 11 with the gate open;

Figure 13 is a perspective view of the lower part of the support of the embodiment of Figures 10 and 11 with the gate closed;

Figure 14 is a perspective view of an alternative control mechanism;

Figure 15 is a cross-sectional view of the control mechanism of figure 14; and,

Figures 16a to c show side views of the control mechanism of figure 14 at different stages of operation.

Referring now to Figures 1 to 6, these show a barrier 10 having an opening and closing mechanism, according to the present invention.

Figure 1 shows the barrier 10 which comprises closure members 11 in the form of a six-bar gate, typically used in, for example, the entrance to a farmyard or field. The gate 10 is pivoted on a support 100 and closes against a support post 14, which carries a latch mechanism 200 for latching the gate in its closed position. In the embodiment shown, the support 100 is installed in a substantially vertical orientation.

The operation of the gate is effected by way of actuation means in the form of a treadle 500. The gate also has a control mechanism (not shown in figure 1), which controls operation of the gate 10 in response to actuation of treadle 500.

Various embodiments of the control mechanism are discussed in relation to figures 7 to 16.

Referring now to Figures 2 and 3, (Figure 2 is a sectional view taken in the direction of arrow 2 of Figure 7) these show sections through lower and upper end portions of the support 100 for the gate. The support 100 has a first, inner elongate support member 114, which is conveniently cylindrical in shape. The support member 114 is rigidly supported on a base unit 104. The support 100 also has a second outer, elongate gate support member 102, here in the form of a cylindrical post, which is mounted preferably coaxial with the inner member 114 so as to be rotatable about its axis relative to the inner member 114.

The support 100 further has a drive member 120 (see figure 3), which is provided coaxially within the inner member 114. The drive member 120 is axially moveable between lower and upper positions, as is described further below.

The gate 10 is secured to the outer post 102 such that pivoting of the post 102 about its vertical axis pivots the gate 10 between its opened and closed positions.

At its upper end 106, the post 102 is closed by a closure member 108 having a cylindrical downward extension 110 terminating at its lower axial end in a cam having a cam surface 112 within the post 102. The cam surface 112 is inclined at an angle to the horizontal of typically 45 degrees. Thus it will be appreciated that the cam surface 112 is elliptical in profile when viewed from an angle normal to said surface. The cam 112 is mounted for rotation with post 102 for opening and closing of the gate.

The inner member 114 has a cam 115 at its upper end portion 116. In effect, the upper end portion 116 is formed at an angle to the horizontal, typically 45 degrees, to form a cam surface 118. The cam surface 118 is generally upwardly orientated such that it opposes the generally downwardly orientated cam surface 112.

The arrangement of the cam surfaces 112 and 118 is such that when the gate 10 is in its closed position, the plane of the cam surfaces are rotationally offset relative to one another by an angle of typically 90 degrees around the rotational axis of the post 102. Again, with the gate in its closed position, the cam surface 112 of the extension 110 abuts and rests on the cam surface 118 of the member 116, but because the cam surfaces are inclined one relative to the other, the weight of the gate applies a torque to the support member 102 through the cam surfaces 112 and 118, such that when the gate is released it swings from its closed position to its open position under the action of gravity. Thus the cam surface 112 rotates relative to cam 118 in order to effect opening of the gate.

In the illustrated embodiment, the gate pivots about the inner member 114 into the plane of the paper (Figure 1) away from the viewer, i.e., in an anti-clockwise direction as seen in Figure 7. During pivoting of the gate towards its open position, the cam surface 112 rides over the cam surface 118 until the two surfaces abut at the same angle to the vertical. During such movement, the support member 102 also moves vertically downwards. The effect is similar to that of a rising butt hinge on a door, in that the action of the hinge causes the door to close under its own weight. However, in the illustrated example, the arrangement of cam surfaces is such that they cause the gate to move from its closed position to its open position.

The drive member 120 is provided to enable the gate to pivot from its fully open position to its closed position. The drive member 120 has a cam 121 formed at its upper end, the cam having a cam surface 122. The cam surface 122 is again inclined at a preselected angle to the horizontal, typically 45 degrees, and lies in a plane angle such that when the gate is in its closed position, the plane of the cam surface 122 is parallel with the plane of the cam surface 112. As a result, it will be appreciated that when the gate is in its opened position, the cam surfaces 122 and 112 are rotationally offset relative to one another by about 90 degrees.

The drive member 122 is activated by a drive mechanism which raises and lowers the drive member 120, and is described further below.

Referring to Figure 3, when the drive member 120 is raised into its uppermost position, its cam surface 122 contacts the cam surface 112 of 110 and raises the latter axially so as to disengage the cam surfaces 112 and 118.

The cam surfaces 122 and 112 thus engage, again in the form of a rising butt hinge, the result being that the weight of the gate 10 causes the cam surface 112 to ride over the cam surface 122, pivoting the gate towards its closed position, until the latch 200 is engaged. At this point, the cam surfaces 112 and 122 abut in a generally co-planar manner.

The drive member 120 is then released (as described further below) and drops back to its lowermost axial position, allowing the post 102 to drop until the cam surface 112 rests on the cam surface 118 ready to urge the gate towards its open position once the latch 200 is released, in the manner described above.

Referring again to Figure 2, this shows partially in cross-section the base 104 and a part of the drive mechanism which raises the drive member 120.

The drive mechanism includes two pulleys 130, 132 which are vertically spaced and mounted for rotation on the post 114. The pulleys are arranged with their rotational axes horizontal. A connection 134 intermediate the pulleys secures a drive cable 136 to the post 114. The drive cable extends from the connection 134 around the upper pulley 132 and then around the lower 130 to run horizontally and around a further pulley 138, mounted with its rotational axis vertical.

Actuation of the drive member 120 is effected by the control mechanism 300, which is discussed in further detail for each of the embodiments of figures 7 to 16.

Figure 4 shows a latch mechanism 200 on the post 14, which is used in a conventional manner to retain the gate latched in its closed position. However, the latch mechanism conveniently includes a motorised drive mechanism 202 which can be actuated remotely in order to open the latch and allow the gate to swing open.

The latch may be operated in response to a control signal issued upon operation of the treadle and/or a portable device, such as a key fob, which can be operated by a user to send a wireless signal to receiver means associated with the drive mechanism 202. The latch can also be manually operated in a conventional manner by lever 203 as will be understood by a person skilled in the art.

Referring firstly to Figures 5 and 6, these show plan and elevation views of a treadle 500 having a base 502 for securing to the ground and two rectangular ramp members 504, 506 hinged together at 508 along one pair of side edges. The opposing side edge of plate 506 is pivoted to the base 502 whilst the opposing side edge 512 of plate 504 is free to move between first and second extreme positions. This is effected by engagement of lateral spigots 514, depending from the plate 504, in slots 516 which are formed in side walls 517 of the base 502 and which allow restrictive movement of the plates 504, 506 between a raised, retracted position, as shown in Figure 6, and a lowered, extended position in which the plates 504, 506 are co-planar or near co-planar.

The treadle is thus operated by pressing down on either or both plates 504 and 506, which effects movement of the spigot 514 in a perpendicular, substantially horizontal, direction. Thus the treadle is operable by the weight of a vehicle being applied to the treadle via a vehicle wheel.

The two plates are biassed by suitable biassing means such as a tension or coil spring, such that they are urged from their lower position towards the raised inverted V-shaped position shown in Figure 6. Typically, the coil spring is

connected between one of the spigots 514 and an anchor on the base 502. A coil spring may be provided for each spigot.

As can be seen best in Figure 5, the free end 512 of the plate 504 is coupled to an actuating cable 520 by way of a first order lever 522, arranged such that depressing the hinged plates 504, 506 from their attitude shown in Figure 6 towards a flattened attitude tensions the cable 520. The lever 522 typically applies a magnitude of 3:1 or 4:1 to the movement. In this regard, one end of the lever 522 is connected to spigot 514 and the opposing end is connected to cable 520.

The tension created in the cable 520 provides the drive for operation of the gate 10 via a control mechanism, which is described in further detail below.

Referring now to Figures 7 and 8, the actuating cable 520 is connected through a tension spring 522 to an actuating rod 524, which is in turn connected to a pawl and ratchet mechanism 526. The latter has a ratchet 528 and a pawl 530, which act to retain the rod 524 in the position to which it is drawn by actuation of the actuator cable 520. An extension block 540 is attached to the rod 524, such that it moves linearly with movement of the rod 524.

The end 140 of the drive cable 136 is secured to the ratchet 528 after passing around the pulley 138.

The operation of the mechanism is now described below.

In normal circumstances, the driver of a vehicle who wishes to pass through the gate, releases the latch mechanism 200 either manually or by way of a remote control.

The gate then pivots from its closed position to its fully open position under the action of the cam surfaces 112 and 118, as described above.

The driver then drives the vehicle through the gate ensuring that the vehicle wheels on one side pass over the treadle 500. The weight of the vehicle depresses the plates 504, 506, thus pivoting the lever 522 and drawing the actuating cable 520 to the right. This draws the ratchet 528 to the right, pulling on the drive cable 136, which raises the drive member 120 to bring the cam surface 122 into engagement with the cam surface 112, raising the latter above the cam surface 118. The action of the cam surfaces 112 and 122 then cause the gate to swing towards its fully closed position under its own weight.

However, in order to prevent the gate closing too soon and perhaps hitting the vehicle, a delay or dwell timer mechanism 600 may be provided.

As can be seen from Figures 7, 8 and 9 the outer post 102 carries a trip arm 602 which, in the closed position of the gate, is in the position shown in Figure 7.

The dwell mechanism 600 has a double acting piston/cylinder unit 604, which has a piston rod 606 extending from the unit 604. The piston rod 606 carries an extension 607 in the form of an elongate member, which in turn has an upwardly extending stop 608 at its end remote from the piston rod 606, and an axially extending slot 609 into which a laterally extending tongue 616 of the extension block 540 engages.

A coil spring 610 is mounted coaxially around the piston rod 606 between a stop and the piston/cylinder unit body, such that as the piston rod is moved from its position shown in Figure 7 towards the right as seen in Figure 7, the spring 610 is compressed.

The trip member 602 is provided with a depending flange 620, which is located on the trip member such that when the post 102 pivots from the closed position to the open position, the dependent flange 620 is not fouled by the stop 608 on the

piston rod 606. Thus, in the open position of the gate, the position of the trip member 602 in relation to the stop 608 is as shown in Figures 8 and 9.

When the treadle is actuated by passage of a vehicle, drawing the actuating cable 520 to the right, the extension block 540 is drawn to the right and as a result, the tongue 616 draws the piston rod 606 to the right, as seen in Figure 7, against the action of the spring 610.

The fluid in the two chambers of the unit 604 flows between the two chambers through a valve 630, which allows free flow of the fluid from the right hand chamber to the left hand chamber as seen in Figure 7, but provides restricted flow in the reverse direction. The effect is that whilst the piston rod 606 and thus the stop 608 is moved freely to the right under the action of the movement of the extension block following actuation of the treadle 500, it is allowed to move to the left only at a controlled rate.

The position of the stop 608 and the depending flange 620 on the trip member 602 are arranged such that when the stop 608 is drawn to the right under the action of the tongue 616 following actuation of the treadle, the stop acts to prevent pivoting of the post 102 and thus the gate 10 from its open position.

Once the vehicle has passed over the treadle 500, tension in the actuating cable 520 is released.

At the same time, the spring 606 having been compressed by the action of the extension block now acts on the piston rod 606 to move the latter and thus the stop 608 towards the left as seen in Figure 7. However, this movement is controlled by the rate of flow of fluid between the two cylinder chambers, as a result of which the stop 608 takes a pre-selected time to clear the depending flange 620, allowing the vehicle to clear the gateway.

Once the stop 608 clears the depending flange 620, the weight of the gate pivots the post 102 towards the closed position under the action of the co-operating cams 122 and 112, as described above.

As the post pivots towards the closed position, the trip member 602 is pivoted towards the position shown in Figure 7 where it engages and releases the pawl 530, allowing the drive member 120 to drop under its own weight to its start position, drawing the ratchet 528 by way of the drive cable 136 into its start position.

The speed of opening and closing of the gate can be controlled by a suitable damping mechanism such as a spring whose tension can be adjusted or a hydraulic damping mechanism which can be adjusted to control the opening and closing speed of the gate.

Alternatively, double acting piston/cylinder unit 604 of the dwell mechanism can be replaced by a drive motor for controlling return axial movement of the extension 607 to release the trip member 602 and allow the gate to close. The drive motor may be operated in response to a control signal issued upon operation of the treadle and/or a portable device, such as a key fob, which can be operated by a user to send a wireless signal to receiver means associated with the drive motor. The same key fob and/or signal (for example, RF) as is used for the gate opening latch mechanism 200 can be used here. However, it would be preferable for different signals to be used to reduce wear and tear on the mechanisms.

It will also be appreciated that drive from the treadle 500 to the drive member 120 can be effected by suitable hydraulic, pneumatic or electromechanical means or other suitable mechanical means, in place of the drive cable 136.

Referring now to Figures 10 to 13, these show a modification to the system of Figures 1 to 7 in which like parts are given like reference numbers. Figure 12 shows the lower end of the support 100 with the gate in its fully open position whilst Figure 13 is a view similar to that of Figure 12 with the gate in its fully closed position.

As can be seen in Figure 10, the support member 114 has a lower end extension 160, which may extend below ground level in the installed system. The drive member 120 is also provided with a lower end extension 162, which extends into the extension 160 of member 114, below the level of the treadle mechanism 500 and possibly below ground level.

A pulley 164 is mounted in a similar position to the pulley 138 of Figure 2, but in this embodiment its pivot axis extends horizontally. The drive cable 136 extends from the mechanism 500 around the pulley 164 and downwardly into the extension tube 160 and is secured to the extension 162 of the drive member 120.

As will be appreciated, in this embodiment raising of the drive member 120 is again effected by a vehicle passing over the treadle and thus drawing the drive cable 136 to the right, as seen in Figure 10. Figure 12 shows the drive member 120 in its lowest position.

When the drive member 120 is raised, a free end 550 of a latch in the form of a first order lever 552 engages in a slot 165 in the drive member 120. The lever 552 is biased to pivot in an anti-clockwise direction to engage the slot 165 when the drive member 120 is raised. The lever 552, therefore, serves to retain the drive member 120 in its raised position.

With the gate in its fully open position, the trip member 602 engages a latch 702 of a latch mechanism 700. The latch 702 is also conveniently a first order lever, which can be rotatably driven in an anti-clockwise direction, as seen in Figure 12, by a drive motor 704 in order to release the trip member 602.

As the gate swings open, the trip member 602 engages the latch 702 and the gate is thus retained in its fully open position. As the vehicle drives over the treadle, the drive member 120 is raised as described above, and the latch 552 engages in the slot 165 of the drive member 120 to retain the drive member in its closed position.

Once the vehicle is clear of the gate, the latch member 702 is pivoted in an anticlockwise direction to release the trip member 602. The latch member 702 can be actuated remotely, by way of the drive motor 704, or manually simply by pivoting the latch member 702.

The latch member 702 may be operated in response to a control signal issued upon operation of the treadle and/or a portable device, such as a key fob, which can be operated by a user to send a wireless signal to receiver means associated with the drive motor 704. The same key fob and/or signal (for example, RF) as is used for the gate opening latch mechanism 200 can be used here. However, it would be preferable for different signals to be used to reduce wear and tear on the mechanisms.

Once the trip member 602 is released, the gate swings closed under its weight, as described above, and at the point of closure, the trip member 602 engages an upstanding flange 554 on the opposite end 556 of the lever 552, pivoting the lever clockwise as seen in Figure 12 and disengaging the end 550 from the slot 165 of the drive member 120. The latter is thus released and falls under the action of gravity and the weight of the gate into its starting position.

It will be appreciated by those skilled in the art that the ratchet mechanism shown in Figures 7, 8 and 9 could also be used here in place of the latch mechanism 700.

In accordance with the above embodiments, it will be appreciated that there is provided a latch arrangement 300 and 700 for holding the gate in an open or closed condition which is distinct from the latching or retaining arrangement 550 which serves to maintain the gravitational potential energy of the gate as required for subsequent operation of the gate. Furthermore there are provided a pair of slots 165, the purpose of which is described below.

Referring now to figures 14 to 16, a pull mechanism is shown for use in accordance with a preferred embodiment of the present invention. The pull mechanism 800 is arranged to be connected as shown in figure 14, such that the cable 136a depending from the treadle 500 enters the pull mechanism 800 at a first end 802 and exits at a second opposing end 804. Thus the pull mechanism is connected in the force path between the treadle 500 and the pulley 164 via respective cable portions 136 a and 136b.

The pull mechanism 800 allows a dual operation of the treadle, for example by way of both a front and rear wheel of a vehicle actuating the treadle in succession. This allows the displacement of the treadle to be used to provide maximal displacement of the gate mechanism via cable 136 for subsequent operations of the gate.

The pull mechanism 800 has six major component parts which comprise housing 806 having opposing side walls 808 and 810; a base 812; a movable body in the form of plate 814; hook member 816; a ramp 817 attached to the base; and spring 818 (see figure 16).

The housing side walls 808 and 810 contact the base 812 either side of a elongate central rise 820. The base 812 thus forms a fixed track upon which the housing 806 can slide in a linear fashion. The slider-type housing 806 has elongate slots 822 extending part-way along the length of each side wall 808 and 810.

The plate 814 is constrained by lateral portions 824 which are received in the slots 822. The plate can thus move relative to the housing by a limited distance defined by the length of the slots 822. The housing 806 and plate 814 thus form a dual slider arrangement, in which the plate can move independently of the housing, which in turn can slide over the bas 812.

As can be seen in figure 15, the plate 814 has a slot 826, in which an end 828 of hook 816 can engage. The hook is pivotably mounted to the housing 806 on rod 830 which is mounted between side walls 808 and 810. The hook can thus pivot into engagement with the plate 814 such that the housing 806 and plate move in unison, or else can be raised free of the plate 814 such that relative movement between the housing and plate is permitted. The hook also has a downwardly extending arm 819 which is attached to the hook by a bolt 821 spaced a distance from pivot 830.

The spring 818 is connected between bolt 832 on the plate 814 and a bolt 834 on the housing and is tensioned to resist tension in the cable 136. The cable end 136a is attached to the plate 814 at fixation point 836 and the cable end 136b is attached to the fixation point 838 on the housing 806.

The housing side walls have second slots 840 which limit the travel of the housing relative to the base. In this regard, the ramp 817 has lateral projections 842 which are located in the slots 840.

The pull mechanism is shown in its start position in figure 16a which corresponds a gate open condition, prior to charging of the gate by the treadle. In this condition, the housing is in its rightmost position such that projection 842 on ramp 817 abuts against the left hand side of slot 840. The plate 814 is in its leftmost position within the housing such that spring 818 is tensioned by the cable 136. The hook is disengaged from the plate 814.

In figure 16b the pull mechanism is shown after a first actuation of the treadle whilst the gate is in its open condition. The plate 814 has moved to its rightmost position within slot 822 and the housing 806 has moved partway along the base 812. In addition the hook has ridden over the end of plate 814 by virtue of the 5 ramped shape of the hook and has engaged within slot 826 in plate 814. Thus subsequent movement of the pull mechanism upon further actuation of the treadle results in movement of the plate and housing in unison.

After the first actuation of the treadle, the drive member 120 is raised such that 10 the lever 550 engages in the first of the two slots 165. This retains the drive member 120 in a first raised position.

In figure 16c, the pull mechanism is shown after second actuation of the treadle, for example by a vehicle's rear wheel, whilst the gate is in the open condition. 15 This represents the fully charged condition in which the gate can be raised to its maximum height. The housing has been pulled to its leftmost position by cable 136a in unison with plate 814. This has caused arm 819 to ride up ramp 817 so as to disengage the hook from the plate 814.

20 The gate is now charged and ready to close upon release of latch 702 (see figure 12). The housing 806 is free to return to the start position under tension of cable portion 136b. The hook drops to the starting position as it rides down ramp 817.

The lever 552 is engaged in the lower slot 165 such that the drive member is held 25 in the uppermost position.

Once released by latch 702, the gate rides down cam surface 122 and closes. When latch 300 is released, the lever 552 can disengage slot 165, allowing drive member to drop such that subsequent reopening of the gate can be achieved by ' 30 cam 112 riding down cam 118.

The two-stage raising of the gate is achieved by provision of a second slot in drive member 120, spaced a predetermined distance from the slot 165 shown in figure 13. Thus the lever 552 acts as a retaining mechanism so as to preserve gravitational potential energy between the first and second treadle actuations.

The above-described gate opening mechanisms do not require any external power sources and the gates can be operated by a pedestrian without difficulty.

One advantage of the above-described gate opening and closing mechanisms is that, in the closed position of the gate, the energy to open the gate is stored in the mechanism in the form of potential energy by virtue of the height of the gate, with the gate support member 102 supported on the cam surface 118. This is achieved by a retaining mechanism incorporating lever 552 as discussed above.

The gate is left in a condition in which energy to open the barrier (in the form of the weight of the gate) is stored in the vertical load between the first and second cams. Other gate opening mechanisms, in which the energy is largely dissipated on the closure of the barrier, require the energy to be inputted to the system (through the weight of a vehicle in contact with the treadle) on approaching the gate, and thus need an energy input mechanism sited some distance from the gate and on both sides of the gate.

The embodiments described above allow the use of only one treadle and control mechanism, which can be placed beneath the gate in the closed position of the latter. This again contrasts with known mechanisms where often two such treadles and control mechanisms are required, one for opening the gate and one for closing. The mechanism according to the present invention has the advantage that it can be installed within the boundary of a property and does not require any portion to be positioned outside the gate opening.