GB2182707A

GB2182707A - Electromagnetic door lock

Info

Publication number: GB2182707A
Application number: GB08527408A
Authority: GB
Inventors: Walter Wilson Hugh Clarke
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-11-07
Filing date: 1985-11-07
Publication date: 1987-05-20
Also published as: GB8527408D0; GB2182707B

Abstract

A door lock of the type which makes use of an electromagnetically generated force for holding fixed and movable parts together. The locking comprises a fixed part (10) for attachment to a door frame (12) and a movable part (14) for attachment to a door (16). The fixed part (10) includes a ferromagnetic plate (32) and a solenoid coil (30). The movable part (14) includes a tubular 30 collet (42), which is fixed at one end relative to the door (16), and a tapered ferromagnetic plug (44) disposed longitudinally within the collet (42) such that energisation of the coil (30) causes the door (16) to be held in its closed position by magnetic attraction between the tapered plug (44) and the fixed plate (32). However, when the door is pulled in an opening direction from its closed position, the free end of the collet (42) is arranged to be caused to ride up the taper of the plug (44) whereby the collet is expanded radially outwardly to bring a projection (48) thereon into engagement with a stop (50) fixed relative to the door frame (12), thereby to prevent further opening movement of the door (16). <IMAGE>

Description

SPECIFICATION Electromagnetic door lock The invention relates to door locks of the type which are adapted to involve the use of an electromagnetically generated force for holding fixed and movable parts together.

An object of the present invention is to provide a lock of the aforegoing type which is simple and cheap to manufacture but yet provides a reliable locking action.

A door lock in accordance with the present invention comprises a fixed part for attachment to a door frame and including a ferromagnetic plate and a solenoid coil, and a movable part for attachment to a door and including a tubular collet, which is fixed at one end relative to the door, and a tapered ferromagnetic plug disposed longitudinally within the collet such that energisation of the coil causes the door to be held in its closed position by magnetic attraction between the tapered plug and the fixed plate, and that, when the door is pulled in an opening direction from its closed position, the free end of the collet is caused to ride up the taper of the plug whereby the collet is expanded radially outwardly to bring a projection carried thereby into engagement with a stop fixed relative to the door frame to thereby prevent further opening movement of the door.

Preferably, the stop is formed by an annular barb or shoulder formed adjacent the free end of the collet and said stop is formed by a shoulder on a bobbin supporting the solenoid coil.

Advantageously, the solenoid coil is disposed within a ferromagnetic tube which projects from the door frame towards the door, and the collet is fixed at said one end to a rigid plate which is itself fixed over an aperture extending right through the door, the door aperture being sufficiently large as to be able to accommodate the tube therewithin in the closed position of the door.

This method of fixing is architectrally attractive and strong; however, surface fixings and/or bracket adaptations for sliding doors are both equally feasible.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a diagrammatic sectional view through one embodiment of a lock in accordance with the present invention; and Figure 2 is a front view of the stationary part of the lock fixed in the door frame.

The illustrated lock comprises a stationary, receiver part 10 which is rigidly fixed to a door frame 12 and a movable part 14 which is adapted to move with the door 16.

The stationary part of the lock comprises a steel plate 18 containing a circular opening 20. One end of the plate 18 is welded to a second plate 22 disposed at right angles to the plate 18. A further plate (not shown) can be welded to the plates 18 and 22 in a plane perpendicular to both (i.e. parallel to the plane of the drawing), this structure being rigidly fixed into one top corner of the door frame 12 by means of screws (not shown). In an alternative structure, the plate 22 and said further plate may be formed integrally from a single piece having a 90" fold.

One end of a mild steel tube 24 is welded in the opening 20 in the plate 18, the other end of the tube 24 carrying an annular mild steel ring 26. Ring 26 can be connected to tube 24 by any suitable method, for example welding, silver soldering, brazing or the like.

An annular bobbin 28, containing a coil 30, is inserted into the tube 24 so as to abut at one end against the annular plate 26. The other end of the bobbin 28 is engaged by a mild steel disc 32 which is held in position within the tube 24 by means of a circlip 34.

The wires from the solenoid coil 30 are passed through a slot (not shown) in the disc 32, the slot being positioned to coincide with the gap in the circlip 34.

Means other than a circlip can be used to hold the disc 32 in place, provided that a magnetic plane is provided in the region of the disc 32 and with good magnetic contact to the tube 24.

The aforegoing assembly provides the receiver (energised) part of the lock.

The other part of the lock, which is carried by the door, comprises a backing plate 36, preferably a metal disc, which is rigidly fixed over the front of an aperture 38 which passes right through the door 16 and is of diameter somewhat greater than the outside diameter of the tube 24 so that the latter tube can be accommodated within the hole 38 in the door, as shown in Fig. 1. Mounted to the plate 36 by means of a flange 40 at its one end, is a tubular collet 42 of length just less than the distance between the plate 36 and the disc 32 in the closed position of the door. Disposed within the collet 42 is a tapered mild steel plug 44 of length no longer than that of the collet 42. The collet 42 contains a plurality (usually 12 or more) of longitudinal slits (not shown) extending from its smaller diameter end adjacent the disc 32 nearly to the flange 40 at the larger diameter end.

The illustrated embodiment is intended to be used at the top corner of the door 16 away from the hinge. As evident from the above description, the hole 38 in the door is sufficiently larger than the outer diameter of the tube 24 to allow the static part of the lock to pass right into the door (in its closed position) and surround the collet 42.

Provided no current is supplied to the coil 30, the door can open and close freely. However, when current flows in the coil 30, the magnetic field holds the tapered steel plug 44 onto the disc 32. If then the door is pulled in the opening direction, the collet 42 is displaced by the door over the plug 44 whereby the front, smaller end of the collet rides up along the tapered surface of the plug 44 and is thereby expanded radially outwardly. The front end of the collet 42 is formed with an annular barb or shoulder 48 which becomes engaged with a shoulder 50 formed on the inner periphery of the bobbin 28 whereby to prevent further movement of the door in the opening direction. The bobbin 28 is therefore made of a strong non-magnetic material, such as brass, and the collet 42 is preferably made of stainless steel.

Thus, the lock will always engage as long as sufficient current is passed to hold the tapered plug 44 against the force required to expand the collet.

In practice a fairly shallow angle of taper for the plug 44 is desirable. However, this can still be enough to heip the door return to its closed position by reverse action on the taper when someone trying to open the door stops pulling.

In some embodiments it may be desirable to include a spring means (not shown) arranged to pull the plug 44 towards the plate 36 in order to assist the reclosing action. This may be achieved, for example, by drilling a blind bore in the back of the plug 44 and holding a tension spring by cross pins, the other end of this spring being fastened to the plate 36. This might, for example, be desirable in applications where fire exit on power failure may be important.

An additional feature of the electromagnetic collet lock is that an unique means of sensing that the lock is closed can be employed. Say the inductance of the energising coil L0 with the door open, it becomes L, (significantly higher than L0) with the door closed. However, L, is significantly lower than the inductance could be (L2) if someone inserted a piece of ferromagnetic material into the aperture, to give the impression to sensing equipment that the door is closed. Thus L, has a singular value which may be detected by a suitable capacitor coupled sensing circuit working at a suitable measuring frequency. The reason L2 is likely to be larger again than L1 is because any spurious insert is likely to make magnetic contact at both ends of the magnetic circuit.

Claims

1. A door lock comprising a fixed part for attachment to a door frame and including a ferromagnetic plate and a solenoid coil, and a movable part for attachment to a door and including a tubular collet, which is fixed at one end relative to the door, and a tapered ferromagnetic plug disposed longitudinally within the collet such that energisation of the coil causes the door to be held in its closed position by magnetic attraction between the tapered plug and the fixed plate, and that, when the door is pulled in an opening direction from its closed position, the free end of the collet is caused to ride up the taper of the plug whereby the collet is expanded radially outwardly to bring a projection carried thereby into engagement with a stop fixed relative to the door frame to thereby prevent further opening movement of the door.

2. A door lock as claimed in claim 1, wherein the said projection comprises an annular barb or shoulder formed adjacent the free end of the collet and said stop is formed by a shoulder on a bobbin supporting the solenoid coil.

3. An assembly comprising a door frame and door fitted with a door lock as claimed in claim 1 or 2, wherein the solenoid coil is disposed within a ferromagnetic tube which projects from the door frame towards the door, and the collet is fixed at said one end to a rigid plate which is itself fixed over an aperture extending right through the door, the door aperture being sufficiently large as to be able to accommodate the tube therewithin in the closed position of the door.

4. An assembly as claimed in claim 3, in ciuding a tensioned spring which is effective between the tapered plug and said rigid plate for biassing the tapered plug towards the rigid plate.

5. A door lock substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

6. An assembly of a door frame, a door and a door lock substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.