Self-sensing actuator

Changes in the impedance of an IPMC may be used to create a self-sensing actuating device [Park et al. (2008)]. An advantage of such a device is that the deformation estimation is an intrinsic property of the actuator, i.e. there is no need to equip separate senors as it can function as a coexisting sensor. The capacitance and the resistance of an IPMC are caused by structural featmes of the Pt electrode particles, such as the space between each particle and the density of the particles. The internal electrical characteristics of the IPMC, especially the resistance and capacitance of the electrodes, are changed with the mechanical deformation of the IPMC. When an IPMC is bent, one electrode surface becomes concave (+), and the other convex (-). 

Fig. 6.5. Controlling of surface structures, a With standard actuator-sensor configurations (A actuator, S sensor), b with linked self-sensing actuators (A/S adaptronic actuator-sensor module)...

The concepts of intelligent and self-sensing actuators mentioned in Sect. 6.1.2 are exemplified below with solid-state actuators. The potential of both concepts is especially easy to recognize and to compare when described in terms of system theory. We will start with the conventional actuator. 

In particular, the decoupling of both sensor and actuator operation for force and displacement reconstruction according to Fig. 6.8 is the main difference in the intelligent actuator concepts depicted in Fig. 6.7. In the case of self-sensing actuators the output y of the sensory path is strongly influenced by the driving quantity X of the solid-state transducer and must be... 

The topic of intelligent actuators and self-sensing actuators will gain growing importance for adaptronic applications, e. g. in relation to structurally integrated electrical actuators. Therefore, we will look at them in more detail from a theoretical system point of view in Sect. 6.9. 

The installation of an additional position sensor is not always possible. Reasons may be costs and/or unavailable space. In this case, the internal sensoric effect displayed by some NiTiCu-alloys may be employed for indirect position sensing [84]. This leads to the use of a self-sensing actuator (cf. Sect. 6.9). In Fig. 6.58 the actuator length Ld of a NiTiCu shape memory wire is plotted against its electrical resistance Rd. The relation is free of hysteresis and is only slightly shifted by the actuators load. 

As self-sensing actuators, the internal sensoric effect can be used for position sensing (see Sects. 6.1.4 and 6.9). Again, this property is useful in small-sized applications where additional sensors cannot be accoimno-dated for space and weight reasons. 

Fig. 6.128. Control of systems and processes, a Customary closed-loop control, b closed-loop control with self-sensing actuator...

F ig. 6.129. Controlling of freeform structures with networked self-sensing actuators... 

All these applications have confirmed the principle of a self-sensing actuator, they have also shown that the linear reconstruction model (6.68) and (6.69) is restricted for small amplitudes of the voltage and force. Furthermore the bridge circuit is strongly affected by external disturbances e. g. from temperature leading to a wrong evaluation of the sensory information. 

The formulation (6.70) and (6.71) permits the application of the state quantity-related approach described in Sect. 6.9.4 for the reconstruction of the mechanical quantities s and F. In this case the reconstruction model of the self-sensing actuator results in... 

Fig. 6.140. Function of the self-sensing actuator concept according to Fig. 6...

The self-sensing actuator concept requires the powerful mathematical machinery of complex hysteresis operators - first for reconstructing the mechanical quantities by means of the measured values of electrical quantities and second for compensating the hysteretic nonlinearities and the load dependency. Whereas robust software tools exist for modeling, identifying and compensating scalar complex hysteretic nonlinearities in practical applications, a considerable amount of research activities is necessary in the field of vectorial hysteresis phenomena to obtain a similar status. 

Ko, B. Tondue, B.H. Acoustic control using a self-sensing actuator. J. Sound and Vibration, 187 (1995), pp. 145 165... 

Jones L. Garcia, E. Novel approach to self-sensing actuation. SPIE Smart... 

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