No abstract

SUMMARYThis paper investigates the stable-running problem of a planar underactuated biped robot, which has two springy telescopic legs and one actuated joint in the hip. After modeling the robot as a hybrid system with multiple continuous state spaces, a natural passive limit cycle, which preserves the system energy at touchdown, is found using the method of Poincaré shooting. It is then checked that the passive limit cycle is not stable. To stabilize the passive limit cycle, an event-based feedback control law is proposed, and also to enlarge the basin of attraction, an additive passivity-based control term is introduced only in the stance phase. The validity of our control strategies is illustrated by a series of numerical simulations.

No abstract

No abstract

No abstract

In order to realize fast and efficient tuning of the proportional-integral-derivative (PID) controller parameters in thermal power plants, this paper thoroughly analyzes the problems existing in the relay characteristic method based on the phase angle margin auto-tuning method (PM method), and proposes an improved PM auto-tuning method for the most common first order plus dead time (FOPDT) model in practical engineering applications. The improved algorithm proposes the design of the target phase angle margin and the method of plant identification. Then, the optimization algorithm is used to calculate the correction coefficient of the setting formula to obtain the PID controller parameters that minimize the integrated time absolute error (ITAE) index of the control system. Finally, through the auto-tuning experiment on the generalized control model of the main steam temperature system in thermal power plants, it is verified that the improved algorithm is superior to the traditional PM method and Ziegler–Nichols method (Z-N method), and can obtain a fast and stable control performance.

Background Morton’s neuroma is a painful enlargement of the plantar digital nerve between the metatarsal heads that causes pain of the forefoot. Several approaches have been used to treat Morton’s neuroma, each of them having distinct advantages and disadvantages. Objectives The purpose of this study was to investigate and compare the clinical outcomes of neurectomy in the treatment of Morton’s neuroma through plantar and dorsal approaches. Materials and methods A total of 20 patients with a mean age of 48.5 ± 13.0 years (range: 19–66 years) who underwent excision of a Morton’s neuroma that did not respond to conservative treatment were retrospectively analysed from June 2014 to June 2021. All the neurectomies were performed using a plantar or dorsal approach. Outcomes were evaluated using visual analogue scale (VAS) scores, American Orthopedic Foot and Ankle Society (AOFAS) scores, the Foot and Ankle Ability Measure (FAAM), and complications. The appearance index (AI) was also used to assess the influence of foot appearance on the quality of life after surgery. Results Eight patients underwent neurectomy by the dorsal approach, and 12 patients underwent neurectomy by the plantar approach. The average follow-up time was 28.9 ± 12.9 months (range: 15–72 months). No statistically significant difference was found between the dorsal and plantar approach groups with respect to postoperative pain measured by the VAS score. The postoperative AOFAS scores and FAAM outcomes were not significantly different between the groups. The complications reported in the dorsal approach group were significantly less than those of the plantar group, mainly discomfort in wearing shoes. The AI of the plantar group and the dorsal group were significantly different. Conclusion The excision of the Morton’s neuroma by both the dorsal and plantar approach resulted in satisfactory outcomes. However, the foot appearance after surgery by the plantar approach had less influence on the quality of life than that using the dorsal approach. Our recommendation is that surgeons should choose the approach they are most familiar with and with which they are most confident in performing. In addition, the plantar approach is recommended if the patient needs a better appearance.

Although numerous investigations have been undertaken to study the impact load between railway wheel and rail in the presence of a single wheel flat, little attention was devoted to the case of multiple flats. In practice, it is not uncommon that one wheel develops more than one flat or each wheel on the same axle has a single flat. In this study an adaptive contact model, a two-dimensional roll-plane vehicle model, and a three-dimensional track model are developed to investigate the wheel-rail impact load due to multiple flats. Unlike the commonly used Hertzian contact model, the adaptive contact model takes into account the asymmetry of the contact patch as the wheel flat enters and leaves the contact patch. Two scenarios of multiple flats are considered in this investigation. One deals with two flats on the same wheel defined by their size and relative position, and the other deals with a single flat on each wheel of the same axle. In each case, the induced impact loads are compared with those due to a single flat. The results suggest that the magnitude of impact force attributed to the second flat entering the contact region is strongly affected by the responses due to the preceding flat, depending upon the flat geometry, relative co-ordinates of the flats and the operating speed. The results further suggest that the length of a flat alone, which is commonly regarded as wheel removal criteria, may not be adequate when multiple flats are present.