A new gap-based obstacle avoidance approach: follow the obstacle circle method

One of the most challenging tasks for autonomous robots is avoiding unexpected obstacles during their path following operation. Follow the gap method (FGM) is one of the most popular obstacle avoidance algorithms that recursively guides the robot to the goal state by considering the angle to the goal point and the distance to the closest obstacles. It selects the largest gap around the robot, where the gap angle is calculated by the vector to the midpoint of the largest gap. In this paper, a novel obstacle avoidance procedure is developed and applied to a real fully autonomous wheelchair. This proposed algorithm improves the FGM’s travel safety and brings a new solution to the obstacle avoidance task. In the proposed algorithm, the largest gap is selected based on gap width. Moreover, the avoidance angle (similar to the gap center angle of FGM) is calculated considering the locus of the equidistant points from obstacles that create obstacle circles. Monte Carlo simulations are used to test the proposed algorithm, and according to the results, the new procedure guides the robot to safer trajectories compared with classical FGM. The real experimental test results are in parallel to the simulations and show the real-time performance of the proposed approach.

Design of Internal Flow Passage of Internal Chip Removal Drill for Suction Type Internal Chip Removal System

Aiming at the current problem that the cutting chips cannot be automatically recovered in the hole-making process of carbon fiber reinforced resin matrix composites, This article first introduces a new type of drilling chip removal technology system-suction type internal chip removal system, which can timely and effectively discharge the powdery chips generated in CFRP hole processing during cutting; Secondly, in view of the problem of the internal runner design of the internal chip removal drill used in the system, this article conducted the following research: 1) Based on cutting experiments and statistical methods, classify the chips produced in CFRP hole making, and give the chip distribution rules; 2) Secondly, on the basis of fluid mechanics, using FLUENT simulation method, on the basis of defining the center distance and center angle of the inner runner for the design of the internal chip removal drill bit, the center distance and the center angle of the inner runner are given. The influence law of the chip removal center angle and the cross-sectional shape of the internal runner on the chip removal effect of the tool internal runner; 2) Based on fluid mechanics, using FLUENT simulation method, on the basis of defining the center distance of the inner runner and the center angle of the inner runner, the center distance of the inner runner, the center angle and the cross-sectional shape of the inner runner are given to the tool The influence law of the chip removal effect of the internal runner; Finally, a suction type internal chip removal system was built, and the experimental method was used to verify the correctness of the internal runner design of the internal chip removal tool.

The equivalent arc ratio for auditory space

The minimum audible movement angle increases as a function of source azimuth. If listeners do not perceptually compensate for this change in acuity, then sounds rotating around the head should appear to move faster at the front than at the side. We examined whether judgments of relative amounts of acoustic motion depend on signal center angle and found that the azimuth of two signals strongly affects their point of subjective similarity for motion. Signal motion centered at 90° had to be roughly twice as large as motion centered at 0° to be judged as equivalent. This distortion of acoustic space around the listener suggests that the perceived velocity of moving sound sources changes as a function of azimuth around the head. The “equivalent arc ratio,” a mathematical framework based on these results, is used to successfully provide quantitative explanations for previously documented discrepancies in spatial localization, motion perception, and head-to-world coordinate transformations.

Exact Solutions for Out-of-Plane Vibration of Curved Nonuniform Beams

The governing differential equations for the out-of-plane vibrations of curved nonuniform beams of constant radius are derived. Two physical parameters are introduced to simplify the analysis, and the explicit relations between the torsional displacement, its derivative and the flexural displacement are derived. With these explicit relations, the two coupled governing characteristic differential equations can be decoupled and reduced to one sixth-order ordinary differential equation with variable coefficients in the out-of-plane flexural displacement. It is shown that if the material and geometric properties of the beam are in arbitrary polynomial forms, then the exact solutions for the out-of-plane vibrations of the beam can be obtained. The derived explicit relations can also be used to reduce the difficulty in experimental measurement. Finally, two limiting cases are considered and the influence of taper ratio, center angle, and arc length on the first two natural frequencies of the beams are illustrated.

Stability criteria for converging shock waves

Two simple analytical criteria are presented to determine approximately the region of (form and radial) stability for converging (shock) waves as function of the perturbation parameters amplitude Δr/R and center angle γ. By comparison with computer calculations these criteria were found to be safe approximations. The criteria may be stated using an index of refraction N = V∞/V(r) for the wave front.