Geared motor-driven lower limb exoskeletons (LLEs) are widely researched to assist paraplegic patients with spinal cord injury in recovering locomotion ability. In order to achieve a compact exoskeleton joint design while avoiding increasing the mechanical complexity of the exoskeleton frame, this study presents a design of an LLE with compact and modular actuation. A synchronous drive and a gear drive as transmissions are used to distribute hip and knee actuators, respectively, ensuring a compact axial width. The modular design of joint actuators enables it simple to separately design or select the ergonomic exoskeleton frames. A paradigm of the LLE design is comprehensively provided, including the requirement analysis, mechanical, electrical and control system design, which can be a reference of the early development of the exoskeleton prototype. The performance of the LLE is preliminarily validated by the benchtop tests including the closed-loop speed bandwidth test and the swing test and one healthy human subject experiments including walking with the LLE disenabling all motors and walking assisted by the LLE. The results of the benchtop tests validate that the LLE has enough bandwidth of closed-loop speed, satisfactory repeatability, high precision, good antijamming capability and strong torque capacity. The results of the healthy human subject experiments validate a harmonic interaction and a good integration between the user and the ergonomic mechanical system, good performance of the electrical and control system in joints motion control of the LLE. The prototype of the LLE smoothly and successfully assists the healthy human subject in walking on the level ground. The proposed LLE is promising to be applied to assist paraplegic patients in recovering the walking ability.
Selective catalytic reduction with NH3 (NH3-SCR) is an effective technique for purifying flue gas by
removing
nitrogen oxides, and the catalyst plays a key role in this technology.
For the purpose of developing novel, highly efficient, green, and
vanadium-free catalysts, SnNb2O6 nanosheets
were synthesized successfully by hydrothermal and solid reactions
and confirmed by XRD and TEM. These nanosheets were first used as
a support for CeO2−δ to prepare environmentally
friendly Ce/SnNb2O6 catalysts for NH3-SCR. These Ce/SnNb2O6 catalysts had more than
90% NO
x
conversion and 98% N2 selectivity at 250–400 °C and a high space velocity
of 120,000 mL/(g·h), which is higher than the per surface area
performance of the previously reported Ce-based NH3-SCR
catalysts. To explore the factors for this increased activity, NH3-TPD, H2-TPR, and XPS data were analyzed in detail.
The results indicated that Ce/SnNb2O6 nanocatalysts
have more acid and oxidative sites than Ce/SnO2 and Ce/Nb2O5. In addition, the surface of Ce/SnNb2O6 contained 39.4% Sn4+ ions, which synergize
with Ce as additional redox sites. The effect of electron transfer
between Sn and Ce at the interface promoted the formation of molecular
oxygen and cycling of redox sites. Kinetic studies showed that Ce/SnNb2O6 had a low apparent activation energy of 38.0
kJ/mol, which reduced the difficulty of the reaction. DFT studies
indicated that the adsorption energy of NH3 in SnNb2O6 was 429.7 kJ/mol, which is much higher than
that of other common supports, meaning that NH3 is much
easier to adsorb on SnNb2O6 nanosheets, therefore
showing higher catalytic performance. Moreover, in situ DRIFTS analysis
showed the changes in the dominant mechanisms: the L–H and
E–R mechanism coexist at 300 °C, while most of the reactions
follow the E–R mechanism at 400 °C. This study can provide
new insights into the development of new Ce-based NH3-SCR
catalysts to control NO
x
emissions from
stationary sources.
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