Showing papers on "Obstacle published in 1986"

Inverse problems for acoustic waves using the penalised likelihood method

Abstract: The authors consider the following inverse problem for scattering of time-harmonic waves by an impenetrable obstacle. Given data obtained from the scattered field at infinity, they determine the location of the boundary of the obstacle. To solve the forward scattering problem, they use the T matrix method, or null field approach. The ill-posedness of the inverse problem is discussed. To solve the inverse problem, an optimal control, or 'data fitting', approach is used, and stable approximate solutions are obtained using a technique known as the penalised likelihood method. Results of a numerical study are presented, showing the effects on the accuracy of the inversion of different types of far field data, various incident fields, and random error in the data. In two dimensions, several different obstacle shapes are considered. An example for an axially symmetric obstacle in three dimensions is also presented.

The downstream flow beyond an obstacle

Abstract: This paper is concerned with theoretical predictions, given the upstream conditions from a rigid obstacle of arbitrary shape, of the downstream flow beyond the obstacle for an incompressible inviscid fluid sheet under the action of gravity. The fluid sheet flows upstream over a level bottom, continues to flow over (or under) an obstacle leading to a downstream region over a level bottom. In the absence of surface tension, a nonlinear st., ady-state solution of the problem is used to predict the downstream values of the free-surface wave height for the full range of the far-upstream Froude number. The general results obtained are then applied to a special case of fluid flowing over a stationary hump leading to a supercritical flow far downstream and detailed numerical comparison is made with available experimental results, with very good agreement.

Concurrent algorithms for autonomous robot navigation in an unexplored terrain

Abstract: Navigation planning is one of the most vital aspects of an autonomous mobile robot. The problem of navigation in a completely known obstacle terrain is solved in many cases. Comparatively less number of research results are reported in literature about robot navigation in a completely unknown obstacle terrain. In recent times, this problem is solved by imparting the learning capability to the robot. The robot explores the obstacles terrain using sensors and incrementally builds the terrain model. As the robot keeps navigating, the terrain model becomes more learned and the usage of sensors is reduced. The navigation paths are computed by making use of the existing terrain model. The navigation paths gradually approach global optimality as the learning proceeds. In this paper, we present concurrent algorithms for an autonomous robot navigation in an unexplored terrain. These concurrent algorithms are proven to be free from deadlocks and starvation. The performance of the concurrent algorithms is analyzed in terms of the planning time, travel time, scanning time, and update time. The analysis reveals the need for an efficient data structure for the obstacle terrain in order to reduce the navigation time of the robot, and also to incorporate learning. The modified adjacency list is proposed as a data structure for the spatial graph that represents the obstacle terrain. The time complexities of various algorithms that access, maintain, and update the spatial graph are estimated, and the effectiveness of the the implementation is illustrated.

A fuzzy logic approach to robotic path planning with obstacle avoidance

Abstract: Robotic path planning with obstacle avoidance is considered. The main objective of the proposed approach is to reduce planning time considerably for "real-time" applications with obstacles of arbitrary configuration. The concept of a minimum required joint motion envelope is introduced to facilitate the representation of the joint kinematic solutions. Near minimum time trajectories are generated through a phase plane analysis. If the planned path is obstructed, then the obstacle geometry is approximated and a suitable projection is found in joint space. A modified path is finally determined to avoid the obstacles. Fuzzy logic is employed to incorporate uncertainty into the algorithmic procedure. Preliminary investigations have been carried out using a PUMA 560 and its associated workspace.

Obstacle monitoring system for unmanned self-traveling object

Abstract: PURPOSE: To improve safety of an unmanned self-traveling object by adding an emergency stop means to an obstacle controller to stop urgently the traveling object via the direct control of an actuator in case the brake control is not applied yet to stop the traveling object even after the traveling object enters a dangerous range of collisions. CONSTITUTION: An emergency stop means 7 feeds back the lever position of a transmission from a move-forward/back sensor 11b' via a transmission interface part and also the speed of the transmission from a speed sensor S11a respectively. Then the control signals are delivered to control directly the actuators (relay valves) of a rear brake and a parking brake in case no control is given to each actuator 15 from a speed controller 14a or a vehicle controller 14c for prevention of obstacles or the stop of the drive of a self-traveling object even after this object enters a dangerous range of collisions where the distance between the traveling object and an obstacle is smaller than the braking distance of the traveling object. Thus the brake is applied for emergency stop of the traveling object. In such a way, a double securing mechanism is used for the unmanned self-traveling object. COPYRIGHT: (C)1988,JPO&Japio

Commanding device for obstacle evading operation of unmanned vehicle

Abstract: PURPOSE: To deal flexibly with a practical processing speed and the distribution state of various obstacles by judging the necessity of obstacle evasion, and performing arithmetic operation upon occasion and putting an unmanned vehicle in evading operation. CONSTITUTION: An evasion necessity deciding device 6 finds the distance between a run course and an obstacle by using information on the run course stored in a run course storage device 2 and judges the necessity of evasion on the basis of the distance value. Further, an evading operation deciding device 7 computes and determine the distance between the obstacle and unmanned vehicle when the deciding device 6 judges that the obstacle detected by an obstacle detecting device 5 needs to be evaded. The necessary controlled variable of this evading operation is calculated by a run controller 3 to control a driving device 4 and information on the obstacle is obtained from the detecting device 5 even after the evading operation is started to judge the normalcy of last evading operation and a change in the state of the obstacle. Consequently, better evading operation is performed and the change in the state is dealt with. COPYRIGHT: (C)1987,JPO&Japio

Obstacle recognizing device for ship

Abstract: PURPOSE:To prevent a collision against an obstacle securely by a small number crew by recognizing the size and kind of the obstacle, the direction of a stationary ship, etc., automatically on the basis of information from an image sensor and setting the best dangerous area against the obstacle. CONSTITUTION:A radar 1 for the ship acquires a reflected echo of a microwave, which is applied as obstacle information to a collision preventing and rescuing device ARPA4, which performs rough collision decision arithmetic. Information on the position of an obstacle against which the ship collides possibly is inputted to an infrared camera processor 3d. The infrared camera processor 3d sends necessary control signals to a camera controller 3a, an infrared controller 3b, and a panning controller 3c respectively to actuate an active night vision infrared image sensor 2. Then the image sensor 2 controls a focus controller 2b and a pan 2e to aim at the obstacle and operates an infrared-ray generator 2d to acquire a video of the obstacle through an infrared camera 2c.

Obstacle processor for unmanned carrying car

Abstract: PURPOSE:To run smoothly an unmanned car, and also to secure the safety by bringing an obstacle detecting function to an adjusting control in accordance with a course condition of the front of an advance direction of the unmanned car. CONSTITUTION:An ultrasonic sensor control device 34 decides whether an obstacle is far or near, based on a result of detection of ultrasonic sensors 30, 30 for detecting the obstacle in the advance direction. When a signal discriminated a far or near distance of the obstacle from the ultrasonic sensor control device 34 is inputted to a CPU 24, whether it is a short distance ineffective indication or not is discriminated. As a result of discrimination, in case of NO, a run of an unmanned car 10 is stopped, and in case of YES, whether it is a long distance ineffective indication or not is discriminated. As a result of discrimination, in case of YES, a deceleration command is generated to the unmanned car 10 and its deceleration processing is executed, and in case of NO, a run processing for continuing self-running of the unmanned car 10 is executed.

Cubic lattice model simulation of an entangled polymer system

Abstract: The motion of nonintersecting chains on a cubic lattice with a super lattice of obstacles is simulated. Center‐of‐mass diffusion coefficients as well as the end‐to‐end vector relaxation times are measured both in ordered and random obstacle fields. Severe differences in dynamical quantities appear as a result of simultaneous obstacle motion and randomization of the obstacle field. The differences indicate a shift of the system to lower obstacle densities. This is interpreted to be due to preferential motion of the end group (snake head) into large holes, rendering the effective tube diameter larger than the average neighbor–neighbor obstacle distance.

Minimum time path planning for robot motion in obstacle strewn environment

Abstract: A new algorithm of minimum time motion planning is proposed for robots operating in the obstacle strewn environment. Structure of the topological passageways is analyzed and represented using a model of slalom situations for which a number of rules is determined. Dynamical system of robot is described in a form of sequential machine. Thls enabled a merger between two kindred algorithms: A* search algorithm, and dynamic programming. An experimental analysis of the simulated mobile robot has confirmed the applicability of results.

Relative hardness characteristic controlling method of suspension for vehicles

Abstract: PURPOSE:To secure a favorable feeling of comfortableness, by detecting the height of an obstacle ahead of a car and, in case of clearing the obstacle in height within the specified range or more than that, reducing or increasing a relative hardness value in a suspension just before it. CONSTITUTION:At the time of car driving, ultrasonic waves of one pulse are transmitted out of an ultrasonic wave sensor 32 installed in a lower end face in and around the front end of a car 1, making it receive the ultrasonic waves reflected out of a road surface 31 or an obstacle 34. And, a distance Hs between a part reflecting the ultra sonic waves of the road surface 31 or the obstacle 34 and a lower end of the ultrasonic wave sensor 32 is calculated whereby the presence of the obstacle 34 is discriminated by comparison of the calculated value with the car level H detected by a level sensor 35. In addition, a distance Hst between an apex Q of the obstacle 34 and the lower end of the ultrasonic wave sensor 32 is found, calculating height Ht of the obstacle 34. And, when the height Ht is within the specified range, a value of the relative hardness characteristic of a suspension 2 is reduced but when it is more than that, characteristic controlling devices 11, 18 and 18a are controlled so as to increase the value.

Guidance controller for unmanned truck

Abstract: PURPOSE:To obtain a guidance controller for unmanned truck which can detect assuredly obstacles and stop automatically the drive of the truck together with simple attachment and simple change of a guide line, by detecting the horizontal shifts of front and rear parts of the truck body from the guide line with reception of a guiding light beam and separating a part of the light beam to an obstacle sensor. CONSTITUTION:A projector 10 is used for projection of a guiding light beam 100 and for setting a guide line AB. A guidance control part 20 of an unmanned truck 12 contains the 1st position shift sensors 22a and 22b and the 2nd position shift sensors 24c and 24d. The projecting position of the beam 100 is detected based on the detection outputs of those 1st and 2nd sensors. Thus the truck 12 can be driven accurately with control along the line AB which is indicated by the beam 100. If an obstacle exists in the traveling direction of the truck 12, the beam 100 is cut by the obstacle. Thus an obstacle sensor 28a and 28b detects the obstacle, and the drive of the truck 12 is stopped automatically.

Detector for underground obstacle

Abstract: PURPOSE:To detect securely whether there is existent pipings, etc., and to prevent damage to it by incorporating an ultrasonic probe in a bit part for shield boring. CONSTITUTION:The ultrasonic probe 1, an obstacle detection part 14, etc., are provided. Then, sediment water 5 which is made liquid is discharged out through between a shield pipe 1 and a drill rod. In this forward movement, the detection part 14 excites the probe 11 through a signal cable 15 to transmit an ultrasonic wave signal 16. At this time, if there is an obstacle 17 within the propagation distance L of the signal 16, its reflected wave is received by the probe 11 and converted into an electric signal, which can be received by; the detection part 14 through the cable 15 and a signal coupling 18. Therefore, if the obstacle 17 is absent, drilling is carried on to the distance L and when the obstacle 17 is present, the drilling is stopped and a proper countermeasure is taken.

Collision predicting device

Abstract: PURPOSE:To prevent malfunction due to the deviation between an advancing direction and a sensor beam output direction by detecting the passing of an obstacle even except at the 1st and the 2nd reference distances, and outputting a collision prediction signal when the relative speed with the obstacle increase above a specific value. CONSTITUTION:An obstacle sensor 7 on a vehicle transmits an ultrasonic wave 21 and a reflected wave from the obstacle 8 is received to detect the distance between the vehicle and obstacle 8. Then a detection point setter 9 which receives the detection signal decides on the 2nd reference distance shorter than the 1st reference distance and puts relay coils L1 and L2 in operation to set plural, e.g. eight obstacle detection points between both reference distances, thereby operating relay coils L3-L10. Then, relay contacts LL1... which respond to the relays L1... and relay coils M1... are connected to a power source 20 in series to constitute a collision predicting decision device 10, thereby putting a safety device 11 in operation only when the contacts LL1... are all made.

Obstacle detector for vehicle

Abstract: PURPOSE:To prevent misdetection of an obstacle due to perspective, by dividing a display unit into several area so as to changes the amplification factor of a received wave signal with a gain amplification circuit for each of measuring time ranges corresponding to the area. CONSTITUTION:A display unit 14 is divided into a plurality of areas 14a-14d in proportion to the distance to an obstacle 6. Then, the amplification factor of a received wave signal of a gain amplification circuit 11 is changed with a microcomputer 1 for each of measuring time ranges corresponding to the areas 14a-14d. The microcomputer 1 compares peak value of the received wave signal with a reference value to judge the presence of the obstacle 6 for each of the areas 14a-14d of the display unit 14 and shows the results on the display unit 14. This can eliminate misdetection of the obstacle 6 due to the perspective while enabling accurate detection of the position of the obstacle 6.

The effects of a flow obstacle on liquid film flowing concurrently with air in a horizontal rectangular duct.

Abstract: The aspect of a liquid film flowing near a flat plate type obstacle was observed, and the liquid film thickness and the entrainment were measured under a wide range of gas and liquid flow rates. The results are summarized as follows : (1) The configurations of film flows near the obstacle are classified according to whether (a) the liquid film climbs over the obstacle or not, (b) the air flows under the obstacle or not, or (c) the liquid film swells or sinks just upstream or downstream of the obstacle. (2) The lower the liquid flow rate, the larger the effect of the obstacle on the film thickness. (3) The generation of entrainment is regulated by the obstacle when the air volumetric flux is high and by the disturbance wave when it is low.

Travel control system of moving car

Abstract: PURPOSE:To attain automatic travelling even in any traveling area by mounting a fault detector on a moving car to search an unknown obstacle, store the searched result in a memory and travel the moving car so as to keep the car away from the obstacle. CONSTITUTION:The unit moving distance of the moving car 1, the increment of a distance to be used for the retrieval of an obstacle and the increment of an angle are previously set by a travel control device 22 and stored in a memory 22b. The obstacle in the traveling area is seatched by an obstacle searching device 18 mounted on the moving car 1 and the position of the obstacle is sequentially stored in the memory 22b. To search a route, the obstacle is searched by adding or subtracting the distance and angle increments to/from a straight line connecting between the current point of the moving car 1 and an objective moving point in a circle defined by the unit moving distance around the current point as its radius on the basis of information stored in the memory 22b, the succeeding moving point to which the moving car 1 may be moved without being interrupted by the obstacle and its advancing direction are determined and then a steering angle and a car speed are also found out. These results are sent to a traveling speed control device 23 to control the driving of DC motors L10, R11. Said operation is repeated successively to travel the moving car 1.

Obstacle avoiding sailing method for ship

Abstract: PURPOSE:To facilitate the setting of a course and to sail a ship by the shortest distance by substituting the spread of an obstacle in a sea area with a set section of grating-shaped measures and selecting a shorter course between courses which are circumscribed and has the smallest number of inflections. CONSTITUTION:The sea area from a present position P0 to a target position P1 is sectioned in a grating shape of measures which have one division of a minimum turn radius corresponding to a specific sailing speed. The spread of the obstacle 1 is substituted with a set of sections 5. Then, two courses which extend from the current position P0 to the target position P1 while circumscribed with the set of sections 5 and have the smallest number of inflections, i.e. P0-P6-P7-P1 and P0-P10-P11-P13-P1 are set and the right-side shorter route is selected. Consequently, the setting of the course is facilitated and the ship is sailed by the shortest distance while avoiding the obstacle.

Upstream influence and separation in flow past obstacles on a BETA-plane.

Abstract: Flow past a cylindrical obstacle in an enclosed channel is examined when the entire configuration is rotating rapidly about an axis which is aligned with that of the obstacle. When viewed from a frame of reference which is rotating with the channel, Coriolis forces dominate and act to constrain the motion so that it is two dimensional. In this paper a uniform flow is forced past the obstacle in a channel which has depth varying linearly across its width. The latter, which is equivalent to the so called BETA plane approximation for geophysical flows, permits waves to travel away from the obstacle, forming a lee wave train behind it. If the dissipation in the system is sufficiently small, some waves can also travel large distances upstream and modify the oncoming uniform flow. Numerical solutions are presented and compared with previous theoretical results which are available in certain limits of the governing parameters. The possibility of the flow separation of certain types of obstacles is also considered.

Obstacle detecting device of unmanned running car

Abstract: PURPOSE:To control efficiently an unmanned running car by providing a means for detecting whether an obstacle is moving or standing still. CONSTITUTION:An obstacle detecting device 6 is constituted of an obstacle detecting system 30 and a dynamic displacement detecting system 30, and by its output signal, a running driving system 10 is controlled. The dynamic displacement detecting system 30 is provided with an input/output control device 38 for receiving an obstacle detecting signal from the obstacle detecting system 20 and bringing a measuring TV device to an operation control by its signal. In this state, an obstacle image which is imprinted by the TV device 31 is supplied to a storage device 34 and a correcting arithmetic device 35 through an image analyzing device 32 and a switching device 33. An image analyzing result inputted to the storage device 34 and an image analyzing result obtained from the correcting arithmetic unit 35 are compared by a comparator 36, and based on its comparison result, a processing arithmetic unit 37 sends a signal of a stop or an advance continuation, etc. to the running driving system 10.

Collision forecast apparatus

Abstract: PURPOSE:To prevent malfunctioning due to deviation between the direction of advancing a vehicle and that of outputting a sensor beam, by comparing with the second reference distance predetermined the distance detected in a specified time after the detection of the first reference distance predetermined is dicriminated CONSTITUTION:First and second discrimination means derive a discrimination output when an obstacle reaches first and second reference distances l1 and l2 on a sensor beam 2 A passage detecting means sets, for example, eight obstacle detection points lA, lBlH between reference distances l1 and l2 and derives an output when an obstacle passes by each of the detection points In response to the output of a second discrimination means, a relative speed between a vehicle 1 and the obstacle is detected when the obstacle reaches the reference distance l2 and a collision forecast signal is issued when the relative speed exceeds a specified value while an output of the passage detection means exists Therefore, the passage of the obstacle by all of the obstacle detection points lA-lH is detected though opponent vehicles 3 and 4 cross the reference distances l1 and l2 accidentally, a forecast signal output means will derive no output, which eliminates malfunctioning

Obstacle detection system

Abstract: PURPOSE:To perform high-precision detection by calculating the distance from a side where plural transducers (TD) are connected to an area where an obstacle is present. CONSTITUTION:A radar used for an obstacle detection system is arranged covering the entire periphery of an automobile 1 and TDs 51 and 53 are provided at both ends of, for example, a rear surface side 2. Then, a pulse counter 22 while starting counting from an initial state sends a range measurement start signal to a radar 20a equipped with the TD51 and a radar 20b equipped with the TD53. The obstacle 14 is near the TD51, so the radar 20a detects the obstacle 14 firstly and outputs a distance signal, which is inputted to a range area arithmetic circuit 24 through a counter read circuit 23a. Then, the radar 20b also detects the obstacle 14 with delay and its range signal is inputted to the circuit 24 through a counter read circuit 23b. When stepwise range signals from the circuits 23a and 23b are coincident with data in the stepwise range information table of the circuit 24, the circuit 24 outputs a warning signal, which is processed 26.