Transceiver provides much-needed feedback

Low power radio expert Radiometrix has supplied its BiM3 radio transceiver modules to enable the easy programming of modern prostheses.

Low power radio expert Radiometrix, in close association with prosthetic limb specialist Blatchford Products, has supplied its BiM3 radio transceiver modules to enable the easy programming of modern prostheses.

Radiometrix has worked closely with Blatchford for a number of years on a range of programming systems for the company's prosthetic limbs.

Radiometrix has a rare understanding of every aspect of modern applications for its low-power radio devices and it was this that helped provide Blatchford with exactly the right radio transceiver for the job.

Healthy people with a full complement of limbs take walking and running so much for granted that they rarely - if ever - analyse what is going on beneath them.

But it's not like that for everyone.

Imagine this: you are walking along but then have to descend a slight slope.

Suddenly one of your legs locks, then skates out of control and over you fall.

Or, you are standing still and you want to move.

Easy? No, because you seem - at least for a few moments - to be rooted to the spot.

These are precisely the problems encountered by people who have lost one or more legs in an accident and who wear a prosthesis instead.

You might think that walking with a "wooden leg" is simple but it is not.

Modern developments have greatly helped though, and between them, Blatchford and Radiometrix have got together to greatly improve the lot of the prosthetic leg wearer.

A modern "wooden leg" is actually anything but.

For a start, it's not made of wood but modern engineering materials.

It does have a "knee" but this cannot twist through the angles that a real knee can.

Nor do the wearer's muscles actuate and control any part below that attachment point to the "stump" so, as the wearer's "load-line" (essentially related to the C of G) changes, as it will whilst walking, the prosthetic leg can either lock or fold (collapse).

If these modes occur at the wrong time, such as slowing down, an accident may be inevitable.

Even if there isn't an embarrassing and painful fall, the wearer's gait can be very strange, for example, twisting or "goose stepping".

Dynamic stability is key.

The key to reducing these unwanted effects as far as possible, and also making it easier to learn to walk, is in ensuring as much control as possible.

Blatchford, with Radiometrix's help, has done just this with the control system of its latest product, the Adaptive Prosthesis.

The main phases of walking that need to be considered and controlled as far as possible are "stance" and "swing".

The Adaptive Prosthesis combines the best features of Blatchford's renown earlier products: a combined pneumatic/hydraulic cylinder - with common actuator rod - to provide "swing" control and "stance" control, respectively.

Previous models used either a pneumatic cylinder or a hydraulic, but not both.

The new cylinder is expensively made in nickel-plated aluminium by Blatchford and its pneumatic end is - essentially - an air spring with good control over its rate.

A tiny stepper motor drives the control valve.

The cylinder is not a power source.

The power derives from the wearer's own remaining musculature which is in the leg stump contained within an inner liner and outer socket which, in turn, is attached to the prosthetic leg.

This cylinder gives the wearer what is termed "spring assist".

The hydraulic end of the cylinder provides the necessary "stance control" with a DC motor-driven rotary valve controlling oil flow over each cycle.

As the "leg" extension increases, so does the resistance in this cylinder.

It acts rather as an automotive suspension damper does, but with extra control, yet gives no appreciable resistance in the "swing phase".

The combined cylinder is mounted between a prosthetic knee and shin, coupled to each via pivots, so allowing controlled bending.

In addition, the Adaptive Prosthesis has a number of other walk modes not previously available in one unit: "stumble detection"; "ramp mode"; "standing mode" and "stairs and descent mode".

The result for both Blatchford and the device's wearers is the "best of both worlds" compared with earlier products.

The Adaptive Prosthesis is more akin to a modern Grand Prix racing car in its engineering and technology, with nickel-plated aluminium, carbon fibre, engineering plastics and advanced control and feedback systems.

The Adaptive Prosthesis is operated by circuitry on a printed circuit board (PCB) which is screwed to the side of the combined cylinder.

There are two sensor inputs: a GMR that measures the actuator rod stroke and a force sensor in a rubber pad on the knee.

Essentially, the PCB and its processor control the motors and valves that adjust resistance and "assist" to the wearer's great advantage - better, safer walking.

Also mounted on the PCB is Radiometrix's BiM3 radio transceiver module.

Each prosthesis is set up to meet individual requirements.

Previously, this had been carried out using a wire link to programme the control circuitry on the PCB.

This had many obvious disadvantages for both programmer and wearer.

More recently, Radiometrix helped out with a wireless one-way radio link.

Though far better, there was still the problem that there was no feedback so that the programmer was just telling the prosthesis what to do, but not getting information on what it was actually doing.

Now that The Radiometrix BiM3 has been chosen by Blatchford's electronics expert and Adaptive Prosthesis Project Development Engineer Andy Sykes, two-way communication is simple.

The proper feedback allows much easier setting up.

When the prosthesis is correctly programmed, the BiM3 module is switched off until any later adjustments are necessary, so as to save power in the three lithium cells that provide energy.

A major reason for Sykes' choice of BiM3 is that it operates on both 869.85 and 914.5MHz frequencies.

It therefore meets the American FCC Regulations for low power radio devices.

This is important to Blatchford, as the company is trying to develop a larger share of the US market for prosthetic limbs.

BiM3 is also compatible with other Radiometrix products which Blatchford also uses.

Commented Sykes: "Radiometrix's BiM3 module is compact, reliable and also operates at a high bitrate (64Kbit/s).

We are not using this full potential at the moment but it is useful to know that there's a bit in reserve".

The BiM3 radio transceiver module offers the advantages of high transmit power and datarates, greatly improved receiver interference rejection and a lower profile, all with reduced power consumption and antenna size.

This makes the BiM3 ideal for use with battery-powered portable and handheld applications requiring the ultimate in miniaturisation.

Two versions are available, covering the European 868-870MHz band and the US 902-928MHz band.

BiM3 features include the following: 869MHz version to EN300 220-3 and EN301 489-3; 914MHz version to FCC Part 15.249; SAW filter for enhanced transmit and receive performance; internal voltage regulator for increased stability; crystal-controlled PLL FM circuitry; datarates to 64Kbit/s; usable range to 120m; full screening; low profile and low power requirements.

Applications for BiM3 include: PDAs, organisers and laptops; handheld terminals; EPOS equipment, barcode scanners and belt clip printers; data loggers; audience response systems; in-building environmental monitoring and control; high-end security and fire alarms; restaurant ordering systems and vehicle data up/download systems.

The BiM3 is a compact 23 x 33 x 6mm.

The transmit power is 0dBm (1mW) nominal with a receive sensitivity of -100dBm at 1ppm BER.

Other salient performance features of this transceiver include a supply range of 2.7-10V, 8mA transmit/10mA receive with a data bitrate of 64Kbit/s maximum.

The receiver image rejection is better than 40dB and the receiver local oscillator leakage is less than -65dBm.

The BiM3 is CE certified by an independent notified body.

Back to top