Study on the Structure and Performance of an Antagonistic Pneumatic Bidirectional Rotary Joint

An antagonistic pneumatic bidirectional rotary flexible joint was developed to improve both safety and environmental adaptability of service robots and associated human interactions. The joint comprises two semicircular rotary actuators with positive and negative symmetrical distributions and a pneumatic brake. As such, it achieves forward and reverse rotations, and its damping and braking are adjustable in real time, enabling it to maintain its position. According to the force/torque balance at the free end of the rotary actuator, the rotation angle static model was established. The relationship between the actuator rotation angle, driving torque, impedance torque, and air pressure was obtained experimentally. The brake airbag was manufactured using additive manufacturing and silicone gel casting technologies. The mathematical model of the braking torque was established next, and the model was verified through experiments. Furthermore, an experimental system was constructed to carry out the air pressure-angle, air pressure-torque, and speed response experiments without the load on the joint. The results have shown that the joint can achieve any position within ± 68.5° when the driving air pressure varies from 0 to 0.30 MPa; the time required to reach the maximum angle was 0.85 s. The joint has shown good adjustable damping characteristics. Lastly, the braking torque reached 4.21 Nm at 0.32 MPa, effectively maintaining the position.

Preparation and Optimization Green Gel Casting Technique for Manufacturing Near-Net-Shape Ceramics Using Genetic Algorithm

Gel casting technique is a promising technology that has ability to produce near-net shape ceramics via using toxic and non-ecofriendly agents. The current work aim to develop green gel casting technique using water as a solvent, agar as a gelling agent, and the microwave thermal treatment instead of cross linker. 8mo l% Yttria stabilized zirconia was selected as a case study to produce near-net shape ceramics. The experimental work involved the preparation of Yttria stabilized zirconia nanoparticles via chemical precipitation method. The effect study of agar ratio, Yttria stabilized zirconia solid loading percent on the physical, mechanical, surface properties of the prepared ceramics and selecting of suitable casting conditions. The study has been found that the microwave thermal treatment develops thermally activated cross linking in the agar aqueous solution leading to higher glass transition temperature for agar. The green combination (agar aqueous solution and microwave treatment) can be used as alternative to (monomer, solvent, cross linker) Companion. Also, using the ultrasonic treatment can effectively eliminate needs for dispersants, also the vacuum de-airing treatment. Yttria stabilized zirconia ceramic with high dimensional accuracy, low surface roughness (Ra=2. 81 nm) can be obtained using an agar ratio of (0.4%) and solid loading of (65%). The sample can be moulded with complex shape and the green gel, also the pre-sintered body is machineable. The sintered samples have a porosity of (31%) and compressive strength of (234MPa). Regression analysis and genetic algorithm are showed that the obtained microhardness, compressive strength, and surface roughness are predictable.

Yttria- Stabilized Tetragonal Zirconia with Superior Mechanical Properties Prepared Using Gel Casting Technology and a Two-Stage Sintering Process

Yttria-stabilized tetragonal zirconia (YTZP) ceramics with high densification and superior mechanical properties were obtained using gel casting technology and a two-stage sintering process. Well-dispersed Nano-sized (94 nm) zirconia slurry with high solid content (45vol%) was prepared for gel casting using Dolapix CE64 as the dispersant. As the dispersed slurry was added epoxy monomer (EGDGE) and polymerization initiator (DPTA), Dolapix CE64 promoted gelling, leading to an abrupt increase in the slurry viscosity. As Dolapix CE64 was added into the slurry, its functional carboxyl groups reacted with EGDGE, resulting in a decrease in gelling incubation time and an increase in viscosity, hence, leading to gel casting failure. The addition of hydroquinone (HQ) into the slurry can be used to delay the polymerization and extend the gel casting working time. After gel casting, the temperature was raised to above 60o C to promote the polymerization, leading to an increase in the green strength.A two-stage sintering process was used to control the grain growth. The first stage sintering temperature was chosen at 1300oC, where the relative density reached 83%. In the second sintering stage, the temperature was lowered to 1240°C and soaked for 24 h to inhibit grain growth (mean grain size of 195 nm) and continue densification to a relative density of above 99%. Vickers hardness of 15.2GPa, fracture toughness of 7.8MPa.m1/2, and flexural strength of 771MPa can be obtained for the sample prepared using gel casting technology with a two-stage sintering process.

A Finite Element Analysis for Improvement of Shaping Process of Complex-Shaped Large-Size Silicon Carbide Mirrors

In the gel-casting process, the proper selection of technological parameters is crucial for the final quality of a green body. In this work, the finite element method is used to investigate the mold characteristics in the gel-casting process, and the typical flow behaviors under different conditions are presented. Based on the distribution characteristics of temperature, pressure and flow field of gel polymer, the simulated results provide some possible reasons for the generation mechanisms of defects. Then, a series of simulations were performed to investigate the effect of process parameters on the molding quality of green gel-cast bodies. The results show that the decreasing loading speed can effectively reduce the number of defects and improve the molding quality. In addition, this paper presents a new technique by applying the exhaust hole to decrease the number of defects and, hence, improve structural integrity. The influence of the loading speed on the mold characteristics is well understood for the gating system with an exhaust hole, which suggests to us appropriate parameters for optimizing the molding design. This work provides a theoretical basis to explicate the generating mechanism of defects involved in the gel-casting process and acquires an optimized technique to produce a silicon carbide green body.