30-08-2014, 01:00 PM
NAVBELT AND GUIDECANE
NAVBELT.docx (Size: 1.78 MB / Downloads: 11)
INTRODUCTION
Recent revolutionary achievements in robotics and bioengineering have given scientists and engineers great opportunities and challenges to serve humanity. This seminar is about “NAVBELT AND GUIDECANE”, which are two computerised devices based on advanced mobile robotic navigation for obstacle avoidance useful for visually impaired people. This is “Bioengineering for people with disabilities”.
NavBelt is worn by the user like a belt and is equipped with an array of ultrasonic sensors. It provides acoustic signals via a set of stereo earphones that guide the user around obstacles or displace a virtual acoustic panoramic image of the traveller’s surroundings. One limitation of the NavBelt is that it is exceedingly difficult for the user to comprehend the guidance signals in time, to allow fast work.
A newer device, called Guide Cane, effectively overcomes this problem. The Guide Cane uses the same mobile robotics technology as the NavBelt but is a wheeled device pushed ahead of the user via an attached cane. When the Guide Cane detects an obstacle, it steers around it. The user immediately feels this steering action and can follow the Guide Cane’s new path easily without any conscious effort. The mechanical, electrical and software components, user machine interface and the prototypes of the two devices are described below.
MOBILE ROBOTICS TECHNOLOGIES FOR THE
VISUALLY IMPAIRED.
Histogram (VFH).
The VFH method is based on information perceived by an array of ultrasonic With the development of radar and ultrasonic technologies over the past four decades, a new series of devices, known as Electronic Travel Aids (ETA’s),was developed. This seminar introduces two novel ETA’s that differ from the ETA’s like C5 laser cane, Mow at sensor, in their ability to not only detect obstacles but also to guide the user around detected obstacles.
Obstacle Avoidance Systems (OAS) originally developed for mobile robots, lend themselves well to incorporation in Electronic Travel Aids for the visually impaired. An OAS for mobile robots typically comprises a set of, ultrasonic or other sensors and the computer algorithm that uses the sensor data to compute the safe path around detected obstacle. One such algorithm is the Vector Field sensors (also called Sonar’s) and a fast statistical analysis of the information. The VFH method builds and continuously upgrades a local map of its immediate surroundings based on recent Sonar data history. The algorithm then computes a momentary steering direction and travel speed and sends this information to the mobile robot. The ultrasonic sensors are controlled by the Error-Eliminating Rapid Ultrasonic Firing (EERUF) method. This method allows Sonar’s to fire at rates that are five to ten times faster than conventional methods.
NAV BELT
The Nav Belt consists of a belt, a portable computer, and an array of ultrasonic sensors mounted on the front of the belt. Eight ultrasonic sensors, each covering a sector of 15˚ are mounted on the front pack, providing a total scan range of 120˚.The computer processes the signals that arrive from the sensors and applies the robotic obstacle-avoidance algorithms. The acoustic signals are relayed to the user by stereophonic headphones. Figure (2), shows the experimental prototype of the device and pictorial representation of it’s concept.
OPERATIONAL MODES:
- The NavBelt is designed for three basic operational modes, each offering a different type of assistance to the user.
Guidance Mode: -
In the guidance mode, the NavBelt only provides the user with the recommended travel speed and direction, generated by the VFH obstacle avoidance algorithm the system attempts to bring the user to a specified absolute target location. The VFH. In this mode, (Vector Field Histogram) method calculates its recommendation for the momentary travel direction from the polar histogram by searching for sectors with a low obstacle density value. Next, the
VFH algorithm searches for the candidate sector that is nearest to the direction of the target and recommends it to the user. The recommended travel speed is determined by the VFH method according to the proximity of the user to the nearest object. The recommended travel speed and direction are relayed to the user by a single stereophonic signal. An important parameter involved in the guidance mode is the rate at which signals are transmitted. When the user is travelling in an unfamiliar environment cluttered with a large number of obstacles, the transmission rate increases and may reach up to 10 signals per second. On the other hand, when travelling in an environment with little or no obstacles, the transmission rate is one signal every three second.
Directional-Guidance Mode: -
In this mode, the traveller uses a joystick or other suitable input devices to define a temporary target direction as follows – when the joystick is in its neutral position, the system selects a default direction straight ahead of the user no matter which may the user is facing. If the user wishes to turn sideways, he/she deflects the joystick in the desired direction, and a momentary target is selected5-mt. diagonally ahead of the user in that direction. In case an obstacle is detected, the NavBelt provides the user with relevant information to avoid the obstacle with minimal deviation from the target direction. The recommended travel speed and direction are conveyed to the user through a single stereophonic signal, similar to the method used in the guidance mode. This mode gives the user more control over the global aspects of the navigation task
ADVANTAGES
NavBelt can detect objects as narrow as 10mm.
NavBelt can reliably detect objects with a diameter of 10cm or more, regardless of the travel speed.
The current detection range of the NavBelt is set for 3mt
DISADVANTAGES
For object with diameter of 10mm, the detection is possible if the objects are stationary or the subject is walking slowly (less than 0.4 m/s).
NavBelt lacked the ability to detect overhanging objects, steps, sidewalks, edges etc. This can be removed by addition of Sonar’s pointing up and down to detect these types of obstacles.
It does not allow fast-motion.
The NavBelt uses a 2-D representation of the environment. The representation of this type becomes unsafe when travelling near overhanging object or approaching bumps and holes.
The above disadvantage can be removed by substantial modifications to the obstacle-avoidance algorithm and to the auditory interface
IMPROVEMENTS
The Nav Belt is currently not able to detect over hanging objects. This problem can be removed by using a camera and a laser scanner attached to a special helmet, which can detect objects according to the user’s head orientation. Adding more sonar’s to the front pack of the Nav Belt (pointing upwards and downwards) can provide additional information.
GUIDE CANE
It can be thought of as a robotic guide dog. The functional components of the GUIDE CANE are shown in the figure. A servomotor, operating under the control of the built-in computer, can steer the wheels left and right relative to the cane. Both wheels are equipped with encoders to determine their relative position. For obstacle detection, the Guide Cane is equipped with ten ultrasonic sensors, and to specify a desired direction of motion, the user operates a mini joystick located at the handle. Based on the user input and the sensor data from its sonar’s and encoders, the computer decides where to head next and turns the wheels accordingly.
FUNCTIONAL DESCRIPTION
During operation, the user pushes the Guide Cane forward with the help of a thumb-operated joystick located near the handle. If the user presses the button forward, the system considers the current direction of travel to be the desired direction. If the user presses the button to the left, the computer adds 90˚ to the current direction of travel and as soon as this direction is free of obstacles, steers the wheels to the left until the 90˚ left turn is completed. Functional component shown in figure (4).
HARDWARE IMPLEMENTATION
Electronic hardware
The electronic system architecture of the Guide Cane is shown in the figure. The main brain of the Guide Cane is an embedded PC/104 computer, equipped with a 486 microprocessor clocked at 33MHz. The PC/104 stack consists of four layers. Three of the modules are commercially available, including the motherboard, the Video Graphics Array (VGA) utility module, and a miniature 125-MB hard disk. Figure(5) also shows the electronic hardware.
ADVANTAGES
It allows fast walking, up to 1m/s while completing complex manoeuvres through cluttered environments.
It can be used to travel or detect staircases.
Easy to handle, and no extensive training needed.
It rolls on wheels that are in contact with the ground, thus allowing position estimation by odometer.
DISADVANTAGES
It uses ultrasonic sensor-based obstacle avoidance system, which is not sufficiently reliable at detecting all obstacles under all conditions.
It cannot detect overhanging objects like tabletops
IMPROVEMENTS
The Guide Cane is currently not able to detect tabletops but it can detect these objects with additional upward-looking sonar. The addition of these sonar is expected to improve the Guide Cane’s performance to a level where a visually impaired person could effectively use the device indoors. Outdoors, however, the implementation of an additional type of sensor will be required to allow the Guide Cane to detect important features, such as sidewalk border’s
CONCLUSION
Both the Nav Belt and the Guide Cane are novel navigation aids designed to help visually impaired users navigate quickly and safely through densely cluttered environments. Both devices use mobile-robotics based obstacle avoidance technologies to determine in real-time, a safe path for travel and to guide the user along that path. Theoretically, conveying to the user just a single piece of information (i.e. a safe direction to walk in) is efficient, fast, and suitable in practise to full walking speeds and even the image of a particular environment could also be transmitted to the visually impaired person (image mode of Nav Belt). It is fundamentally different from the existing ETA’s (Electronic Travel Aids) that, at best, only inform the user about the existence and location of obstacles but do not guide the user around them.