Homogenous ERF

Despite the attention paid to the particulate or dispersion type ERF in the preceding sections (mainly on account of its fast response time and potential for industrial adaptronics), it is the liquid crystal (LC) polymer type that has provided the first commercial application of ERF. 

The Asahi-Castor walker [126] has been devised for patients with walking problems. Clutches similar to those in Fig. 6.73 are filled with a grease like LC polysiloxzine plus dilutant, the characteristics of which are typified in Fig. 6.75. Since no particles are present and the zero volt viscosity is large (fslOPas) there is httle sedimentation and good stability provided the mixture does not crystalise at low temperatures (f 10°C). 

The clutches are fitted to the rear wheels of a zimmer type of frame and, because of the low current demand (IpA/cm of electrode area) can adapt to patient stumbling or run away down a slope or, enable the assembly to act as a trainer - self adaptable to the weight of the patient. Also, the sensors can pick up any irregular movement in gait to procure a safe situation. 

About 2kV/mm is required to produce 8kPa of shear stress at a few hundred s shear rate and a two wheel braking torque of 16 Nm. The draw back to further adaptronic application is the 20 to 80 ms time constant of shear stress to voltage and possibly the Wiesenberg effect arising due to rotation of the polymer at high shear rate. 

The brakes are about 10 cm diameter x 1.5 cm long with a control current at 200 J,A via a CPU, supplied from a 6 V battery. The fluid is not abrasive. 

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