GB2372065A - Manually extendable and retractable security post - Google Patents

Abstract

The security post, for use in car parks, town centres etc., comprises a tubular post 1 accommodated in a close fitting sleeve 2 for movement between a first extended position and a second retracted position, where it is located within the sleeve which itself is located below ground level. The sleeve is fixed to a base plate 3 to which a flanged tube 4 is also secured and to which, in turn, a nut element 6 is secured. A leadscrew 5 extends vertically through the nut and is rotatably secured to the post via a bearing assembly. The leadscrew is formed from a twisted bar with a cornered cross-section and the leadscrew and nut mechanism is designed so that it is non-self-sustaining, with the margin by which the mating threads exceed the minimum criteria for being self-sustaining being at least 50%. The post may be locked in the raised position by a lock pin that engages an end plate fixed to the end of the leadscrew, with the release of the lock pin allowing the post to fall to its retracted position under the effect of gravity.

Description

TITLE: SECURITY POSTS DESCRIPTION FIELD OF INVENTION The present invention relates to manually operated security posts.

BACKGROUND TO INVENTION In such as car parks, and for access control purposes generally, e. g. in town centres, at stadia, etc, one or more retractable posts, or bollards, can be useful for raising and lowering selectively to prevent or permit access, perhaps particularly vehicular access, say limit in favour of authorised personnel and/or vehicles and/or against unauthorised use.

Known devices of this kind, as installed, and whether of powered or manual types, usually comprise a fixed member typically as a tube located in the ground with its upper end open substantially at ground level, a movable member typically a post slidably mounted for vertical movement within the tube from a lower position at least substantially enclosed within the tube and an upper position upstanding therefrom.

Known manual types generally have some form of handle for lifting the post, support means for maintaining the post in its upstanding position, and separate locking means for securing the post in its upstanding position.

Known such support means can be a removable pin or catch securing the post to the tube as in GB2275288 or GB2305199; or such as a cross bar affixed to an elongate shaft, which shaft is secured to the post and is rotatably manoeuvrable into a position such that the cross bar abuts against a fixed surface attached to the tube in the ground and maintains the post in its upstanding position as in GB2268207 or GB2290571.

For either or both of these types of support means, locking is known by preventing the support means from being moved, usually in two positions, namely with the post fully up or fully down. Typical requirement is for two distinct operations to move between post lowered and raised positions, or vice versa, firstly removing the locking means and secondly manipulating the support means.

SUMMARY OF INVENTION An object of the present invention is advantageously to mitigate such requirement of manual security posts or bollards, specifically by way of providing a support mechanism that allows locking in any raised position and allows moving immediately after unlocking without needing a secondary operation.

A suitable movement mechanism involves two co-operating parts both of which require to be held in order to prevent relative movement.

For a lead-screw type mechanism of non-self-sustaining nature, suitable operative requirement is different from such as car-jacking systems that are self-sustaining and always require positive movement of the normal movable operating part.

My co-pending patent application GB 0103958 proposes non-selfsustaining leadscrew-and-nut mechanisms for use in automatic retractable security posts or bollards normally operated by powered drive means, typically of electric motor and gearbox type.

Preferred such leadscrew and nut mechanisms have the following leadscrew characteristic : < CosaTan.................................. Equation 1 where :

g coefficient of friction for the post system/mechanism a = flank angle # = lead angle and : . = Tan' [Lead/7td2]...................... Equation 2 where :

Lead = number of starts x thread pitch d2 = basic pitch diameter The general principle of leadscrew and nut mechanisms is, of course, that if either one is held fast and the other rotated then the rotating element must move relative to the fixed element in a direction perpendicular to rotation, but not otherwise. If the mechanism is maintained such that the nut is held fixed and the leadscrew is orientated vertically, then rotating the leadscrew in one direction will cause the leadscrew to rise, and turning the leadscrew in the other direction will cause the leadscrew to lower.

Where the conditions of Equation 1 are met, i. e. the leadscrew-andnut mechanism is non-self-sustaining, and the nut is prevented from turning, the leadscrew must rotate to move axially. When the leadscrew is released for rotation, the force of gravity alone can be enough to cause the leadscrew to spin back down through the nut to its original position. If a force equivalent to or greater than gravity is applied in the opposite direction, for example, by pulling the leadscrew, and the leadscrew allowed to rotate, then it will turn in the nut and rise. Of course, if the leadscrew and the nut are prevented from turning, then their relative positions will be maintained whatever force is applied, and the system is effectively locked.

In an automatic security post or bollard, a powered drive mechanism will apply torque to the system (via either the nut or leadscrew), and applied torque will be translated into force perpendicular thereto, hence cause relative movement of the leadscrew through the nut.

The equations that govern torque are as follows : Torque (TR) required to raise a load W is TR = [Wd2/2] [ (CosaTan +p)/ (Cosa-pTan)]............... Equation 3 Torque (TL) required to lower load W is

TL = [Wd2/2] [ (p-CosaTank)/ (Cosa + pTan)]............... Equation 4 The value of 11 for typical leadscrew systems is in the range 0. 150.3, and the value of a = 30 is typical for an acme thread. In a system based on such an acme leadscrew of a typical 20mm basic diameter, the corresponding minimum value for CosaTan. (from Equation 1 above) would be achieved by a nominal lead (axial movement for one complete turn) of 11-22mm, thus a 1-start thread of 11mm pitch or a 2-start thread of 5. 5mm pitch, etc-a 1-start thread of 22mm pitch or a 2-start thread of 11mm pitch, etc.

Whilst such minimum CosaTank values have duly been confirmed as representing practical design criteria for an automatic powered system, same has not proved to be reliably viable for manual operation. A modest plus-margin for the value of CosaTank was anticipated at least for manual operation, in order to counter the effects of possible contamination, e. g. sand, dust, etc. , in the system causing increase in the effective coefficient of friction for the system and onset of self-sustaining characteristics.

Surprisingly, it has been established that reliably viable manual operation is best achieved with a very much larger than anticipated plus

margin for CosaTan,, and this invention provides for such plus-margin to be of the order of 50%, even preferably 75% or more.

A suitable leadscrew and nut for this purpose could be either machined or thread rolled or equivalent, and a practical value for the nominal lead for a 20mm core diameter leadscrew would be at least 35mm.

Whilst this obviously affects the mechanical advantage of the leadscrew-and-nut mechanism, this does not need to be high. Unlike such mechanisms as essentially self-sustaining vehicle jacks to lift high loads by translation of radially applied torque in the nut to achieve slow lifting in the vertical direction, a typical post hereof would be relatively lightweight, say of the order of 10Kg, and so can readily be pulled up by hand in an acceptable time of say 10 seconds or less. The result for practising this invention is being able to specify a correspondingly very high lead.

Threads with such very high leads can conveniently be achieved by twisting an elongate member of initially uniform suitably shaped crosssection, i. e. rather than machining a shaft or otherwise cutting or forming a thread. In one embodiment a very high lead leadscrew is formed by twisting a substantially square section bar. The resulting leadscrew has a flank angle, a, of 45 , basic root diameter (d2) equivalent to the maximum circle contained within the sides of the square, and a pitch determined by the number of twists applied. In one example, a 10mm square bar was twisted two full turns to give a pitch of 120mm and a lead of 480mm.

A two-start leadscrew would be formed by twisting a rectangular section bar, a three-start by twisting a triangular section bar, a six start by twisting a hex section bar, etc.

Also according to the above equations, a 10mm square section bar twisted two full turns to give a lead angle of 86 can have a coefficient of friction of 10. 8 (p = CosaTanÂ.), i. e. significantly higher than before. One advantage of this is that the system would still be non-self-sustaining even in the presence of high levels of friction-contributing contamination.

Another advantage of such a leadscrew is that the nut function can be performed by a square hole cut in a quite thin section plate, as there is no requirement to move the leadscrew by applying a radial force, thereby being significantly easier and cheaper to produce than a machined or otherwise formed thread of a nut proper.

Manually operated security posts or bollards hereof may be provided with biasing means for biasing the post/tube towards its upright position, say using a compression spring, although other biasing means may be used such as gas cylinders, constant tension spring or extension spring. The provision of a biasing means can ensure that little, if any, effort is required by a user to lift the post into its raised position.

BRIEF DESCRIPTION OF DRAWINGS One specific embodiment of the invention will now be described and shown, by way of example, in and with reference to the accompanying diagrammatic drawings in which : Figure la shows a vertical section through a front elevation of a security post or bollard, with some details omitted for clarity; Figure lb shows an enlarged vertical section through the front elevation of the bearing assembly; and Figure 2 shows in more detail a twisted bar type leadscrew and cooperating nut element.

DESCRIPTION OF ILLUSTRTED EMBODIMENT Referring to Fig 1, a retractable tubular post 1 is accommodated in a close fitting sleeve 2 for movement between a first extended position not shown) and a second retracted position (shown). The sleeve 2 is fixed to a base plate 3 which base plate 3 also has secured thereto a flanged tube 4 that acts as attachment plate for nut element 6. Leadscrew 5 provides both locking means and moving means of post 1.

The leadscrew 5 extends vertically through the nut element 6 and protrudes into the bearing assembly. Thrust bearing 7 is supported by thrust plate 8 which is immovably fastened to leadscrew 5 and supports the post 1 at a fixed internal cross-plate thereof.

Main collar 9, which is held in place between thrust plate 8 and lock cam 10 by nut 11 provides a running surface between the leadscrew 5 and the main bearing 12. Spacer 13 sets the relative position of the lock cam 10 to the lock 14.

In the position shown, the lock cam 10 is prevented from turning by the lock pin 15, the leadscrew 5. As the lock cam is immovably attached to the leadscrew 5, this is also prevented from turning and thus the post is locked. If lock pin 15 is removed by undoing the lock, then lock cam 10 is able to spin and hence the leadscrew 5 is allowed to rotate in the bearing 12. As leadscrew 5 rotates, the leadscrew 5 moves through the nut element 6 as nut element 6 is immovably fastened to flanged tube 4,.

The leadscrew 5 is prevented from being removed by flange plate 16 which abuts against the leadscrew nut element 6 when the post is in the raised position. Handle 17 provides the lifting means for the post.

When the post 1 is in the lowered position, the outer tube 2 can be sealed by rotating lid 18 about pin 19. Rectilinear flange extends around the upper perimeter of tube 2 for lower surface abutment thereof against the ground level.

Generally, embodiments of the present invention are seen as applicable wherever there is to be provided a retractable bollard, typically comprising a tube to be located in the ground with its upper end open and located substantially at surface level, a post slidably mounted for vertical movement within the tube from a lower position at least substantially enclosed within the tube, locking means to secure the post in both the lower and upper position, a support means extending longitudinally within the tube and means to prevent the post from being removed other than by authorised personnel.

Claims (22)

1. CLAIMS 1. Manually extensible and retractable security post comprising parts c-operating for relative extending and retracting movement by mating threads that have flank and lead angles that satisfy minimum criteria for being non-self-sustaining, and selectively operable locking means for allowing relative rotation of said parts or preventing it at least in the extended state of the post, wherein the margin by which said mating threads exceed said minimum criteria for being self-sustaining is at least 50%.
2. 2. Security post according to claim 1, wherein said criteria include a trigonometric relationship involving the product of the cosine of the flank angle and the tangent of the lead angle that is at least 0.5.
3. 3. Security post according to claim 2, wherein said product is at least 0.75.
4. 4. Security post according to any preceding claim, wherein mating threads produce a lead in mutual rotation of the parts that exceeds 35 mm.
5. 5. Manually raisable bollard comprising a security post according to any preceding claim with one of its said parts for vertical said relative movement.
6. 6. Bollard according to claim 5, wherein the locking means is operable to hold said one part in its raised position.
7. 7. Bollard according to claim 6, wherein said one part will lower by gravity after release operation of the locking means.
8. 8. Security post or bollard according to any preceding claim, wherein the parts comprise a leadscrew extending within and through a fixed tube, and a mating nut secured to the top of the tube.
9. 9. Security post or bollard according to claim 8, wherein the leadscrew is of twisted bar having a cornered cross-section.
10. 10. Security post or bollard according to claim 9, wherein the nut is of plate or sheet form apertured to match said cross-section.
11. 11. Security post or bollard according to claim 8,9 or 10, wherein the tube and the leadscrew supports an extendable and retractable hollow post member as such that retracts about the tube.
12. 12. Security post or bollard according to claim 11, wherein the leadscrew at its extension beyond the nut carries a thrust plate that supports the post member at an internal cross plate of the post member.
13. 13. Security post or bollard according to claim 11 or claim 12, wherein the post member has a handle at its end by which the post member and the leadscrew are manually pulled for desired post/bollard extension.
14. 14. Security post or bollard according to any one of claims 8 to 13, wherein the leadscrew carries a lock cam beyond the nut.
15. 15. Security post or bollard according to claim 14, wherein the lock cam comprises an end-plate fast with the leadscrew and a co-operating lock pin selectively engaging the end-plate.
16. 16. Security post or bollard according to claim 15, wherein the lock pin is operable from a fixing internal of the end of the post member for its selective engagement and release of the end-plate.
17. 17. Security post or bollard according to any one of claims 12 to 16, wherein the leadscrew passes through a bearing fixed beyond the thrust plate.
18. 18. Security post or bollard according to claim 17 with claim 16, wherein the bearing is between the thrust plate and the end-plate.
19. 19. Security post or bollard according to any preceding claim, wherein all other components are within a sleeve.
20. 20. Security post or bollard according to claim 19 with claim 8, wherein the sleeve extends from bottom flanging of the post.
21. 21. Security post or bollard according to claim 19 or claim 20, wherein the sleeve has an openable lid.
22. 22. Security post or bollard arranged and adapted to operate substantially as herein described with reference to and as shown in the accompanying drawings.