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Apical vowels are widely observed across Chinese dialects, such as the rime of [sɹ̩55] 'think' in Mandarin Chinese, which is a syllabic approximant homorganic to its preceding sibilant. The apical vowels in Hefei Mandarin differ from those in Mandarin Chinese and most other languages in three aspects: (i) there are three phonetic apical vowels [ɹ̩], [ɹ̩ʷ], and [ɻ̩] while others usually have one or two, (ii) the alveolar apical [ɹ̩] appears after both homorganic and non-homorganic consonants, e.g. [sɹ̩] vs. [pɹ̩], and (iii) there is a phonological contrast between an unrounded apical [ɹ̩] and a rounded apical [ɹ̩ʷ], e.g. [sɹ̩] vs. [sɹ̩ʷ]. The articulatory properties of the three apical vowels were examined in this study using ultrasound techniques and the results revealed that: (i) the commonalities of tongue gestures for the apical vowels include a retracted tongue root, a lowered tongue dorsum or blade, or both, together with a coronal constriction implemented with the blade and/or the tip; (ii) lip gestures are involved in distinguishing the three apical segments; (iii) the three segments each have its distinct articulatory gestures within a speaker that cannot be simply attributed to the influence from their preceding consonants, with [ɹ̩] and [ɹ̩ʷ] involving a grooving in the front part of the tongue and [ɻ̩] involving a retraction of tongue body in the back region of the vocal tract; (iv) the articulatory gesture of [ɹ̩] after a homorganic consonant, e.g. in [sɹ̩], is similar to that after a non-homorganic consonant, e.g. in [pɹ̩], suggesting an independent articulatory target for this segment. [ABSTRACT FROM AUTHOR]

Walking in real-world environments involves constant decision-making, e.g., when approaching a staircase, an individual decides whether to engage (climbing the stairs) or avoid. For the control of assistive robots (e.g., robotic lower-limb prostheses), recognizing such motion intent is an important but challenging task, primarily due to the lack of available information. This paper presents a novel vision-based method to recognize an individual's motion intent when approaching a staircase before the potential transition of motion mode (walking to stair climbing) occurs. Leveraging the egocentric images from a head-mounted camera, the authors trained a YOLOv5 object detection model to detect staircases. Subsequently, an AdaBoost and gradient boost (GB) classifier was developed to recognize the individual's intention of engaging or avoiding the upcoming stairway. This novel method has been demonstrated to provide reliable (97.69%) recognition at least 2 steps before the potential mode transition, which is expected to provide ample time for the controller mode transition in an assistive robot in real-world use. [ABSTRACT FROM AUTHOR]

This paper presents the design of a gas-actuated anthropomorphic arm prosthesis with 21 degrees of freedom and nine independent actuators. The prosthesis utilizes the monopropellant hydrogen peroxide as a gas generator to power nine pneumatic type actuators. Of the nine independent actuators, one provides direct-drive actuation of the elbow, three provide direct-drive actuation for the wrist, and the remaining five actuate an underactuated 17 degree of freedom hand. This paper describes the design of the prosthesis, including the design of small-scale high-performance servovalves, which enable the implementation of the monopropellant concept in a transhumeral prosthesis. Experimental results are given characterizing both the servovalve performance and the force and/or motion control of various joints under closed-loop control. Index Terms--Monopropellant, myoelectric, pneumatic, prosthesis, transhumeral.

This paper proposes a new approach to the design of a robot actuator with physically variable stiffness. The proposed approach leverages the dynamic characteristics inherent in a pneumatic actuator, which behaves in essence as a series elastic actuator. By replacing the four-way servovalve used to control a typical pneumatic actuator with a pair of three-way valves, the stiffness of the series elastic component can be modulated independently of the actuator output force. Based on this notion, the authors propose a control approach for the simultaneous control of actuator output force and stiffness. Since the chievable output force and stiffness are coupled and configuration-dependent, the authors also present a control law that provides either maximum or minimum actuator output stiffness for a given displacement and desired force output. The general control and maximum/minimum stiffness approaches are experimentally demonstrated and shown to provide high fidelity control of force and stiffness, and additionally shown to provide a factor of 6 dynamic range in stiffness. [DOI: 10.1115/1.2745850]

This paper proposes a structure and control approach for the energy saving servo control of a pneumatic servo system. The energy saving approach is enabled by supplementing a standard four-way spool valve controlled pneumatic actuator with an additional two-way valve that enables flow between the cylinder chambers. The ''crossflow' valve enables recirculation of pressurized air, and thus enables the extraction of stored energy that would otherwise be exhausted to the atmosphere. A control approach is formulated that supplements, to the extent possible, the mass flow required by a sliding mode controller with the recirculated mass flow provided by the crossflow valve. Following the control formulation, experimental results are presented that indicate energy savings of 25-52%, with essentially no compromise in tracking performance relative to the standard sliding mode control approach (i.e., relative to control via a standard four-way spool valve, without the supplemental flow provided by the crossflow valve). [DOI: 10.1115/1.2718244]

This paper presents a control methodology that enables nonlinear model-based control of pulse width modulated (PWM) pneumatic servo actuators. An averaging approach is developed to describe the equivalent continuous-time dynamics of a PWM controlled nonlinear system, which renders the system, originally discontinuous and possibly non-affine in the input, into an equivalent system that is both continuous and affine in control input (i.e., transforms the system to nonlinear control canonical form). This approach is applied to a pneumatic actuator controlled by a pair of three-way solenoid actuated valves. The pneumatic actuation system is transformed into its averaged equivalent control canonical form, and a sliding mode controller is developed based on the resulting model. The controller is implemented on an experimental system, and the effectiveness of the proposed approach validated by experimental trajectory, tracking. [DOI: 10.1115/1.2232689]

The stable simulation of high-stiffness surfaces remains a challenge in impedance-type haptic simulations of mechanical environments. In this paper, the authors propose an approach to achieving a stable, high-stiffness surface in a haptic interface by leveraging the open-loop properties of pneumatic actuators. By using the open-loop component of the actuator stiffness as a primary component of stiffness simulation in a haptic interface, the system requires a comparatively small component of simulated stiffness from the closed-loop control of the actuator. A passivity analysis is presented describing how the presence of an open-loop stiffness enhances the range of passivity of haptically simulated high-stiffness surfaces. Experimental results both with and without a human operator are presented that demonstrate the effectiveness of the approach and its enhanced passivity relative to motor-actuated devices. Index Terms--Haptic interface, passivity, pneumatic actuation, stability, stiffness.