Variable-temperature single-crystal X-ray experiments have been performed on the
thiourea pyridinium chloride, bromide, and iodide inclusion compounds. Two phases were
found for the chloride, three for the bromide, and two for the iodide. As previously reported
for the bromide, at room-temperature all three halides were found to form orthorhombic
crystals in space group Cmcm. For each compound, the pyridinium cation is disordered in
the square cross section thiourea channels. On cooling, the chloride undergoes a phase change
between 200 and 230 K to give an orthorhombic form in Pbca with the a axis doubled and
the pyridinium ions partially ordered. The bromide undergoes a phase change between 170
and 165 K to a partially ordered form in space group Cmc21 with the a axis tripled. A second
phase change occurs between 140 and 150 K to a fully ordered phase in space group P21
cn
with cell dimensions approximately the same as the room-temperature form. The iodide
undergoes a single-phase transition at 120−130 K to a fully ordered form isomorphous with
the low-temperature form of the bromide. The phase transitions have also been studied by
VT 2H NMR of the perdeuteriopyridinium salts. These data have been correlated with the
XRD data and with models for the motion of the pyridinium cation.
This paper proposes a conclusive scalable model for the complete actuation response for
ionic polymer metal composites (IPMC). This single model is proven to be able to
accurately predict the free displacement/velocity and force actuation at varying
displacements, with up to 3 V inputs. An accurate dynamic relationship between the force
and displacement has been established which can be used to predict the complete actuation
response of the IPMC transducer. The model is accurate at large displacements and can
also predict the response when interacting with external mechanical systems and loads.
This model equips engineers with a useful design tool which enables simple mechanical
design, simulation and optimization when integrating IPMC actuators into an application.
The response of the IPMC is modelled in three stages: (i) a nonlinear equivalent electrical
circuit to predict the current drawn, (ii) an electromechanical coupling term and (iii) a
segmented mechanical beam model which includes an electrically induced torque for the
polymer.
Model parameters are obtained using the dynamic time response and results are presented
demonstrating the correspondence between the model and experimental results over a large
operating range. This newly developed model is a large step forward, aiding in the
progression of IPMCs towards wide acceptance as replacements to traditional actuators.
This paper proposes an adaptive trajectory tracking control strategy implemented on a parallel ankle rehabilitation robot with joint-space force distribution. This device is redundantly actuated by four pneumatic muscles (PMs) with three rotational degrees of freedom. Accurate trajectory tracking is achieved through a cascade controller with the position feedback in task space and force feedback in joint space, which enhances training safety by controlling each PM to be in tension in an appropriate level. At a high level, an adaptive algorithm is proposed to enable movement intention-directed trajectory adaptation. This can further help to improve training safety and encourage human-robot engagement. The pilot tests were conducted with an injured human ankle. The statistical data show that normalized root mean square deviation (NRMSD) values of trajectory tracking are all less than 2.3% and the PM force tracking being always controlled in tension, demonstrating its potential in assisting ankle therapy.
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