Akimasa Suzuki

Indoor positioning for moving objects using a hardware device with spread spectrum ultrasonic waves

Moving objects, especially autonomous mobile robots, require information of indoor self-location with high accuracy to reach their destination safely and correctly. In this study, we aimed to measure the indoor position of a moving object using SS (spread spectrum) ultrasonic waves, and we discussed the accuracy of the moving distance measured using a newly developed hardware device. In the case of static object, we showed that because of the noise tolerance of SS waves, a distance up to 20 [m] could be measured between a transmitter and a receiver on cm-order. To detect the SS ultrasonic signals, correlation calculations were carried out between a range of received waves and same range of replica signals; the replica signals were the same as the transmitted SS signals. Popular positioning systems using SS electrical waves employ signal acquisition to calculate coordinates of objects from correlation values and signal tracking to measure the relative shift of distances of moving objects. It is difficult for the system using SS ultrasonic waves to continue tracking because of the decrease in the self-correlation value due to the Doppler effect that acted on a moving object. To solve this problem, we proposed a tracking method for keeping correlation values by limited range of correlation calculations. In this study, for obtaining real-time updates of positional information from the relative shift, an experiment of distance measurement was also conducted using a newly developed hardware device that was used to carry out signal acquisition and the proposed tracking method. The results show that real-time signal tracking with our method could be realized, same as existing software between +/- 0.5 [m/s]. This paper reports that we can expect self-localization of robots using this system.

Monocular 3D palm posture estimation based on feature-points robust against finger motion

The usability of wearable augmented reality (AR) systems would improve by letting users arbitrarily display virtual information on their palm and simultaneously manipulate it as tablet computers or smartphones. To realize such interaction between users and virtual information, we aim to robustly estimate 3-D palm posture against finger motion. This is based on the assumption that finger motion is separately estimated from palm posture and applied to manipulation of displayed information. In addition, the capability of electric sources, sensors, and processors are very limited in wearable computers. For this reason, by using a monocular camera and estimating palm posture from only a few image feature-points, we achieve an efficient estimation that satisfies real-time constraint on wearable computers. The accuracy and the robustness of our method are demonstrated by qualitative and quantitative comparison with a widely-used cardboard maker. Additionally, we confirmed that our method is run on a mobile computer at the average of 12.44 msec per frame.

Measurement accuracy on indoor positioning system using spread spectrum ultrasonic waves

This paper describes significant factors on spatial error distribution measured in a given indoor space with a local positioning system which utilizes spread spectrum ultrasonic waves generated by narrow directional ultrasonic transmitters. The positioning error has interestingly been discussed from the viewpoints of the dilution of precision (DOP) and the ranging error due to the transmitter directional characteristic, mainly. The indoor 3-D position is calculated by means of an algorithm using distances from the transmitters located at the four corners of the ceiling to a mobile receiver. From the result of these experiments, it has been usefully found that the positioning error can be more largely influenced on the DOP of vertical direction than it of horizontal direction and that its average is of 3.43[cm] rms for all 3-D measurable points. These findings obtained from the work imply that the 3-D indoor positioning can be realized with an acceptable centimeter-order of precision. Moreover, they suggest that it has to be considered from the viewpoints of not only the ranging error, which could be yielded by the distance measurement, but also the DOP, which is inevitably obtained by a geometrical arrangement relative to the transmitters and receiver.

Real-Time Distance Measurement for Indoor Positioning System Using Spread Spectrum Ultrasonic Waves

The fields of application for position information have been expanded along with developments in the information-driven society. Outdoor position information systems such as car navigation systems that use the global positioning system (GPS) have spread widely. On the other hand, indoor position information is also important for humans and robots for self-location and guided navigation along routes. However, as the signals from satellites seldom reach indoors, it is hard to convert a directly outdoor positioning system to an indoor one. Therefore, systems that use sensors such as pseudolites (Petrovsky et al., 2004), infrared rays (Lee et al., 2004), or ultrasonic waves (Shih et al., 2001) have been investigated for use in indoor positioning.

An information addition technique for indoor self-localization systems using SS ultrasonic waves

In this paper, we propose an information addition technique for a 3-D indoor positioning system using spread spectrum (SS) ultrasonic waves, and evaluate its effectiveness. The system can position a target with high resolution, noise tolerance, and an ability of implementing CDMA by SS code using a limited number of transmitting channels. An M-sequence is employed as the SS ultrasonic code. Our aim is a positioning system for self-localization of people and robots; the location of a receiver installed on a target can be measured with SS signals from transmitters mounted in the positioning area. To evaluate the effectiveness of the proposed technique, an experiment to measure the distance from transmitter to receiver was conducted with the original hardware used with this technique. In this experiment, 4-bit information in a period of the M-sequence, generated by an 8-bit shift register, was applied. The result showed that the distance from transmitter to receiver and the added information can be detected at the same time. This experiment demonstrated the effectiveness of the information addition technique for SS ultrasonic waves.

Code division positioning by continuous signals using spread spectrum ultrasonic waves

Indoor real-time positioning is required in order to realize self-localization for autonomous mobile robots. In particular, accurate control in plural mobile robots requires 3-D coordinate information. This paper presents the positioning accuracy and response time for a 3-D real-time indoor positioning system which uses continuous spread spectrum ultrasonic signals that are generated and detected using inexpensive all-purpose transducers, and a Code Division Multiple Access (CDMA) communication system. For application with moving targets, we propose signal acquisition and tracking using continuous signals in analogy to the already effective Global Navigation Satellite System (GNSS). The proposed calculation algorithm for coordinate acquisition is based on the Newton-Raphson method for continuous signals. The calculation time and accuracy of this method is verified by conducting a positioning experiment. The results show that the positioning error is less than 50 mm in a 4000 mm by 4000 mm experimental space with 4 transmitters. Moreover, the maximum response time to update a result is 80 ms, displaying the efficacy of this system for robot navigation.

Verification of CDMA and accuracy on echo ranging system using spread spectrum ultrasonic signals

This paper proposes the echo ranging system with spread spectrum ultrasonic signals for automobile robots. The spread spectrum signals have noise-proof property and an ability of code division multiple access (CDMA). To verify them on reflected waves, an experimental system for indoor echo ranging dealing with spread spectrum modulations was installed on original PCI hardware connected PC, and experiments for verification of CDMA and measurement accuracies were conducted. Results of the experiments indicated usefulness of the echo ranging system with spread spectrum ultrasonic signals.

Distance measurement system using stereo camera for automatic ship control

A long distance measurement system using a stereo camera mounted on a rotation control device is proposed for automatic ship control, and the performance of the system is presented to verify the usefulness of it. As a solution to prevent ship operators from maritime accidents owing to their strain for a long period, the distance measurement system is often required to automatically control the posture or berthing of a ship. Here, we discuss the system structure suitable for used environment and its experimental results. From the experiment conducted to imagine the distance measurement necessary to altering the posture and translational motion between a ship and its facilities, the average error for the range of 20 to 100 m was less than 1 percent.