Piezoceramic actuators promote security

Simon Powell, Business Development Director Servocell, examines the impact of piezoceramics on the security industry.

The increased availability of advanced encoding, encryption and identity systems means that we now have an unprecedented level of access control and audit capability.

Implementation of such technologies onto networks makes integration with local or remote control centres extremely simple, at least until it becomes necessary to actually permit entry through any form of physical barrier.

Up until the 1990s, solenoids were the primary method of changing locks' status.

A key disadvantage of the solenoid is that it requires a large initial current to begin the motion of the slug at its core and then generally requires a high level of power to keep it in position.

A neat solution to the power crisis in solenoids is the use of magnetically latched devices; however these can be defeated by the use of vibration and also make the condition of the lock uncertain in the event of a loss of power, rendering them unsuitable for applications such as emergency exits.

Through the 1990s the cost of small motor and gearbox assemblies dropped dramatically, primarily due to Chinese manufacturers, but the smaller a motor goes, the lower its efficiency.

Ironless rotor devices are very effective, getting a lot of power from a small space, but put your mobile phone on vibrate and you see the battery life shrink dramatically.

As with solenoids, motors need an inrush current to get them started and will quickly drain a battery if they are stalled.

Piezoelectric materials are not new, having been discovered in the 19th century, but recent developments have changed dramatically the potential they offer the security industry.

The principal behaviour of the material, typically a combination of lead, zirconium oxide and titanium oxide with a few rare materials added, comes from the poling of elongate crystals.

As these crystals are rotated by an electric field, the bulk material changes shape, whilst volume is conserved.

The change is very small in the bulk material, but the development of benders using principles similar to bimetals gave significant improvements.

However, even with bender technology the movement is small, typically 0.2-0.5mm.

Patents filed by PBT in Harlow in 1998 describe how to make a device with movement of about 1.5mm using low cost construction techniques.

Piezoceramic actuators are small capacitors and their shape change is a function of the stored charge.

With a capacitance of less than 100nF a bender moving to its maximum deflection at 200V will consume just 2mJ.

This low current is important because it allows these devices to receive their power over spare wires in the existing wiring on a company's local area network (LAN), or via inductive couplings.

Similarly the telephone line with its 48V supply can only deliver a very limited amount of current: too little for motors and solenoids but ample for piezoelectric devices.

It is not all plain sailing because the gains in movement come at the expense of force, with usable outputs generally below 1N.

So it is not possible to take a traditional lock construction and simply drop in a piezo solution, and this has been a major barrier to adoption.

The launch in 2003 of the Servocell Active Latch has paved the way for a whole new generation of high reliability, low power locks.

Using a patented mechanism the actuator's role is simply to catch and turn a larger locking blade that then causes a moving plunger to be restrained.

The Active Latch can be used to either disconnect a handle from a lock mechanism, or to interact with another part of a mechanism to change its behaviour.

Piezo technology offers the lock designer and user a whole new scenario in terms of lock design and access management.

For the lock designer, electronic cylinders, case locks and rim latches can be made to work from coin cells, and operate for many thousands of cycles.

This permits the designer to get rid of the large battery box that is such a prominent feature on all existing surface mounted locks.

The neat form factor of the actuators also opens up the possibility for more locks in places where traditional solutions are too bulky or power-hungry, such as banks of lockers and remote locations.

For higher security it is also possible to put multiple locks around the part to be secured to interlock a mechanical system.

A good example of this is the multipoint locks used in UPVC doors.

Adding locks at random locations makes it much harder for an intruder to locate and defeat them.

When used as "mechanical transistors" Active Latches can restrain very high loads without any increase in electrical power consumption, taking on the role of motorised or magnetic bolts.

The power saving is appreciable, but it also makes it practical to run such systems from low cost wiring, or even to bring the power to the lock via the key, perfect for access in remote locations, such as farm buildings or manhole covers.

In situations where a definitive failed condition is required, either to keep things in or let people out, piezo-based systems can be permanently powered and will discharge to the default condition when the power is cut by an appropriate alarm.

By connecting the access control and lock technology into the building's LAN infrastructure new locks can be added simply by plugging into the network, or logging them in on a wireless connection.

Of course, this assumes that adequate encryption has been implemented by the system administrator.

In construction the advantages are reduced installation cost and configurable integration.

Through the use of long-life compact batteries, systems that would normally have to be installed with a power hinge and edge drilling can be installed as battery systems, or take their power via an inductive coupling in the door frame.

The evolution of these little locking islands means that it is a short step to adding a unique identifier to each using off-the-shelf devices, like the ubiquitous Dallas one-wire chips.

With this capability added in it is possible to reconfigure spaces and their associated security at will.

New developments in Internet protocol chips have made it possible to web enable just about anything, making overrides and privileges easily adaptable from any location.

Not only is piezo technology the perfect partner for biometric and other advanced validation technologies, it promises to bring higher security with less inconvenience.

A simple example is the replacement of all traditional handles with active handles in a house.

At night, the doors are closed and each room becomes secure.

In the morning one command calls them all to engage and behave like normal doors.

Connect the alarm clock to the network and this can be done automatically.

The ability of piezo solutions to be very compact also means that bleach cupboards, filing cabinets, stair gates and patio doors can all be secured and released by the network.

Another key area in which networks are taking over is the car.

Using systems such as CANbus, the traditional door lock can be replaced with a piezo equivalent.

The power consumption of the locks never mattered with petrol engines, but when the power source is battery or fuel cell the savings in weight and power adds to the usable range of the vehicle.

Piezo technology remains more costly than a motor for single point applications running on mains power, but as soon as the installation moves to networks and remote power supplies the advantages of piezo become clear.

Given that electronic access control will continue to become smarter and more integrated, it seems clear that the new generation of locks will rapidly augment and then replace the more traditional approaches.

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