Bending movement

Fulcrum technique Utilizes a bending movement principle to create a force on the bit to counteract reaction forces that are tending to push the bit in a given direction. 

FIGURE 1.10 Time lapse photographs showing bending movement of bimorph-type actuator (two active electrodes) made from polypyrrole and a porous membrane separator, and activated by 1.5 V potential difference between the polymer electrodes. 

Figure 16.2 Symmetrical and asymmetrical stretching and bending movements in chemical bonds.

The most diffused actuating configuration, in which these materials are used, is represented by the so-called unimorph bilayer bender. This kind of actuator consists of a film of active material coupled to a passive supporting layer. The bilayer structure is operated within an electrochemical cell, having a liquid electrolyte in which the device is immersed. The active polymeric layer of the actuator works as one electrode of the cell, while a counter electrode and a third reference electrode are separately immersed in the electrolyte. One end of the bilayer is constrained, while the other is free. The potential difference applied between the electrodes causes red-ox reactions of the conducting polymer. Since the CP and the passive layers are mechanically interlocked, when the polymer swells/shrinks the passive layer, which can not modify its dimensions, transforms the CP linear displacement into a bending movement of the structure [238-242]. Very similar is the bimorph structure. In this case the passive layer is substituted by a second CP film and they work in opposition of phase. 

Figure 8 Bending movements of a thin fiiament (a compiex of F-actin with tropomyosin and troponin) interacting with myosin fragments in the presence of ATP, where F-actin was iabeied with fiuorescent dye molecules to make it visibie under a fiuorescence microscope (a) inactive state in the absence of calcium ions (b) active state in the presence of caicium ions undergoing fast and large bending movements. The sequential micrographs were taken on 10 /u,m filaments at interval of 0.15 sec (a) and 0.10 sec (b1) and (b2). (From T. Yanagida, M. Nakase, N. Nishiyama, and F. Oosawa. Nature 307 58, 1984. With permission.)...

Another study reports on the fabrication of an ionic polymer-metal composite membrane actuator in cantilever beam geometry that can perform an extensive bending movement (more than 100°) and that can remain curled up under constant voltage (Dai et al. 2009). 

First, the statistical theory - a theory in which only the global swelling is of interest - is reviewed. By refining the scale, two different mesoscopic models are presented first, the chemo-electro-mechanical transport model and second, a continuum model based on porous media. These models are capable of describing the changes of the local variables concentrations, electric field, and displacement. So, e. g., by the application of an electric field, a bending movement of the polymer gel can be realized which is in excellent correlation with experimental investigations. 

Fig. 2 (a) Bilayer device scheme in solution formed by a conducting polymer film and a nonconductive film, (b) Bending movements of a triple layer conducting polymer/tape/conducting polymer (Reproduced from Garcia-Cordova et al. (2011), with permission of the Royal Society of Chemistry)... 

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