Different parameters (air pressure, quantity of minimum quantity lubrication (MQL) oil, position of nozzle, etc.) of an MQL system have different effects on the milling force and milling temperature. The cutting force and cutting temperature, which are closely related to lubrication and coolant, play significant roles in improving/reducing the cutting quality of a workpiece and extending/shortening the tool life. The present work investigates experimentally the effects of different MQL parameters (air pressure, quantity of oil consumed, and position of the nozzle) in end-milling titanium alloy (Ti–6Al–4V). The experimental results show that the penetrating ability of MQL oil mist has a significant effect on the milling forces and milling temperatures. When the values of air pressure and spraying distance were either too large or too small, it is not good for oil mist to penetrate into the contact zones. The spraying angle of the nozzle position has a minimal impact on the penetration ability. Conversely, the amount of oil delivery is the most important part of MQL application. The minimum quantity of oil consumption can be obtained. The results will help to select optimum MQL parameters in end-milling titanium alloy.
Sit-to-stand (STS) motion is an important daily activity, and many post-stroke patients have difficulty performing STS motion. Previous studies found that there are four muscle synergies (synchronized muscle activations) in the STS motion of healthy adults. However, for post-stroke patients, it is unclear whether muscle synergies change and which features primarily reflect motor impairment. Here, we use a machine learning method to demonstrate that temporal features in two muscle synergies that contribute to hip rising and balance maintenance motion reflect the motor impairment of post-stroke patients. Analyzing the muscle synergies of age-matched healthy elderly people (n = 12) and post-stroke patients (n = 33), we found that the same four muscle synergies could account for the muscle activity of post-stroke patients. Also, we were able to distinguish post-stroke patients from healthy people on the basis of the temporal features of these muscle synergies. Furthermore, these temporal features were found to correlate with motor impairment of post-stroke patients. We conclude that poststroke patients can still utilize the same number of muscle synergies as healthy people, but the temporal structure of muscle synergies changes as a result of motor impairment. This could lead to a new rehabilitation strategy for poststroke patients that focuses on activation timing of muscle synergies.
Most users of prosthetic hands must rely on visual feedback alone, which requires visual attention and cognitive resources. Providing haptic feedback of variables relevant to manipulation, such as contact force, may thus improve the usability of prosthetic hands for tasks of daily living. Vibrotactile stimulation was explored as a feedback modality in ten unimpaired participants across eight sessions in a two-week period. Participants used their right index finger to perform a virtual object manipulation task with both visual and augmentative vibrotactile feedback related to force. Through repeated training, participants were able to learn to use the vibrotactile feedback to significantly improve object manipulation. Removal of vibrotactile feedback in session 8 significantly reduced task performance. These results suggest that vibrotactile feedback paired with training may enhance the manipulation ability of prosthetic hand users without the need for more invasive strategies.
Humans are capable of associating actions with their respective consequences if there is reliable contingency between them. The present study examined the link between the reliability of action consequence and the readiness potential (RP), which is a negative potential observed from about 1–2 s prior to the onset of an action with electroencephalography. In a condition of constant outcome, the participants’ voluntary action always triggered beep sounds; thus, they were able to perceive the contingency between their action and the sound. In contrast, in a condition of inconstant outcome, the participants’ actions only triggered the sound in half the trials. We found that both the early and late RPs were larger in the condition of constant compared to the condition of inconstant outcome. Our results showed that the RPs preceding the voluntary action reflected the reliability of action consequence. In other words, the action-effect contingency enhanced neural activities prior to the action.
Minimum quantity lubrication is an alternative to realize machining titanium alloys both economically and ecologically. In order to apply minimum quantity lubrication more efficiently, an investigate of the effects of the operating parameters involving oil supply, compressed air supply, and nozzle orientation is required. This article focuses on the oil supply rate of minimum quantity lubrication and aims to identify the effects of the minimum quantity lubrication applications with different oil supply rates in high-speed end milling of Ti–6Al–4V. The experiments were conducted by adjusting the oil supply rate from 2 ml/h to 14 ml/h, and cutting force, surface roughness, tool wear and failure mode, and tool wear mechanism were discussed. The results indicate that the increase of the oil supply rate effectively reduces cutting force and surface roughness, but after 10 ml/h the reduction is no longer significant. Increasing oil supply has growing penetration depth along the cutting edge, and by increasing the oil supply rate the length of the chipping edge can be notably reduced. For an insufficient oil supply rate (2 ml/h∼10 ml/h) chipping on the cutting edge introduced by diffusion wear is the main tool rejection reason, but at 14 ml/h no diffusion wear is found and the uniform flank wear is dominant, owing to reduced cutting temperature.
Body representation refers to perception, memory, and cognition related to the body and is updated continuously by sensory input. The present study examined the influence of goals on body representation updating with two experiments of the rubber hand paradigm. In the experiments, participants moved their hidden left hands forward and backward either in response to instruction to touch a virtual object or without any specific goal, while a virtual left hand was presented 250 mm above the real hand and moved in synchrony with the real hand. Participants then provided information concerning the perceived heights of their real left hands and rated their sense of agency and ownership of the virtual hand. Results of Experiment 1 showed that when participants moved their hands with the goal of touching a virtual object and received feedback indicating goal attainment, the perceived positions of their real hands shifted more toward that of the virtual hand relative to that in the condition without a goal, indicating that their body representations underwent greater modification. Furthermore, results of Experiment 2 showed that the effect of goal-directed movement occurred in the active condition, in which participants moved their own hands, but did not occur in the passive condition, in which participants' hands were moved by the experimenter. Therefore, we concluded that the sense of agency probably contributed to the updating of body representation involving goal-directed movement.
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