Locking up future access

4 min read

Tom Shelley reports on some novel latches that are bringing about a revolution in access control

New electromechanical latching mechanisms can secure tonnes of force using power supplied by four AA batteries. The latest units, already in pilot production, should sell for around £5 each. They are hermetically sealed in laser-welded enclosures with bellows seals. Target markets are locks. The devices are suitable for industrial, lodging, commercial and domestic applications. Because prices are so low and robustness is so high, applications range from bicycle locks through keyless office and factory access control systems to safes. Servocell's micro-powered AL1 piezoelectric latching device, first revealed in Eureka's November 2004 edition, is already being used to prevent lorry trailers being driven away from loading ramps before loading is finished (see box). It has also been designed into a retro-fittable door lock that can withstand some four tonnes of force on the shaft. This is achieved by taking the AL (Active Latch) concept - using a small force to release a latch that controls a much larger force one stage further. In this case, when the active latch is not energised, turning the door handle pushes down an arrangement that presses in the tongue of the latch and causes a comb to engage against the teeth of another comb, with about 20mm2 of hardened steel pressed against another 20mm2 of hardened steel. If the active latch is energised, the tongue of the latch cannot be pushed in, causing the mechanism to be pushed aside so that the teeth of one comb pass between the teeth of the other, allowing the door to be opened. The whole door handle and lock arrangement is retro-fittable to any door using bolts at the top and bottom. It could easily work with radio frequency tags or other keyless systems. Servocell chief executive Simon Powell says: "With our technology, we can kill the key." Servocell is actively seeking manufacturers to develop the product under licence, but Powell says that his company is prepared to manufacture the device itself if necessary. It recently raised some £4.7 million from a flotation on the AIM market. Estimated selling price from DIY outlets is about £75, while commercially available electro-mechanical locks normally sell for around £125 to £200, he says. Even more remarkable is Servocell's new active latch, the AL2, which is totally protected against the environment over the range -25 to +60[degrees]C. Powell told Eureka that his original version had rubber seals, but as he explained: "To water molecules, polymers are just a crowded street for them to walk through." The unit is 10mm wide, 14mm high and 50mm long including the emerging contact pin. Its latching mechanism is based on balls being pressed against the inside of a metal injection moulded stainless steel cone. If the piezo actuator is off, spring force causes the conical part of the control pin to move past the balls - pressing them through the sides of a plunger by the cylindrical part of the same control pin. They engage with the stainless steel cone and prevent the plunger being pushed down further. If the piezo actuator is energised, moving the plunger assembly pushes the pin back so that the balls are adjacent to a small diameter of the pin. With the plunger in this position, the balls are pressed inwards against the pin by the stainless steel cone and the plunger may be fully depressed. The mechanism is 12mm long. Adaptive electronics read the condition of the actuator and provide the right amount of charge for each operation. By doing this, the electronics are also able to calculate the temperature of the device and the voltage required to drag the actuator back to its start position. The actuator stroke is 1.7mm and the AL2 has a working stroke of 3.7mm with 1mm of free play. The device is rated at 1 million operations and the actuator has been tested to 800 million operations. By a simple change of geometry, the latch can be made normally blocked or normally free. It can thus be powered to allow movement or to block movement. When powered to block movement it can be incorporated into fail safe systems so that release occurs in the event of power failure. Sufficient power could be provided by a solar cell 25mm square, with a super capacitor used for storage. Intended applications run from hotel door lock and security applications down to post boxes, bicycle locks, wheel clamps and padlocks. Powell says: "By combining the latches with low power radio, they stop being just a dumb piece of security. They become nodes in a network that can inform you if batteries are going down so you don't get locked out." The first AL2 devices are being hand assembled in a batch of 2,000, many of which are already booked for customers. Full scale production will start at the end of the year. Servocell Eureka says: A combination of electronics and multi-stage mechanical ingenuity has produced inexpensive, strong locks that run on small amounts of power Pointers * Micro power is required to unlatch a retro-fittable door lock able to withstand up to 4 tonnes of force * Latches are hermetically sealed and can be powered for up to 1 million operations by 4 AA batteries. * OEM price is 10,000 plus quantities is expected to be about $10 each Latch key prevents drive-off accidents Castell Safety International has launched an interlocking solution that prevents the release of lorry air brakes until warehouse loading bay doors have been closed. This is to prevent accidents to loading staff, caused by trailers being driven away from loading bays before the loading/unloading process has been completed. The company's new 'Salvo' solution combines Castell's Salvo Susie air brake locks with its new keyless door interlock, Gallant, designed with Servocell's AL1. Once a trailer is in position against the loading doors of the warehouse, its air brakes are disconnected to prevent the lorry being moved until the loading/unloading process is properly completed. The Castell Salvo Susie is locked in place on the airline coupling, to ensure that the trailer cannot be moved, at which point the key is released. The operative can then insert the key into Castell's control box adjacent to the bay door. This activates the Gallant lock mounted on the door. Only when the lock is activated can the loading bay doors be opened for loading/unloading to begin. Once the process has been completed, the doors are locked, the is key removed from the control box and drivers are then able to unlock the airline coupling in order to reconnect the brakes and move their vehicle. The new keyless door interlock solution can be used in a variety of other warehouse bay door applications. Suitable for applications worldwide, the system will be of particular relevance to the US and Asian markets where most warehouse doors are operated manually rather than electronically.