01-05-2013, 04:34 PM
ROBOTICS IN SOCIAL BY USING NAVBELT
[attachment=53319]
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 computerized devices based on advanced mobile robotic navigation for obstacle avoidance useful for visually impaired people. This is Bio engineering 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 traveler 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 GuideCane, effectively overcomes this problem. The GuideCane 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 GuideCane detects an obstacle, it steers around it. The user immediately feels this steering action and can follow the Guide Can a new path easily without any conscious effort.
The motion of a blind traveler in an unfamiliar environment is somewhat similar to that of a mobile robot. Both have the physical ability to perform the motion, but are depended on a sensory system to detect obstacles in the surroundings, and to relay the information to the control system (human brain or motion control computer). In both cases, reliable obstacle system is mandatory for fast and safe motion.
MOBILE ROBOTICS TECHNOLOGIES FOR THE VISUALLY IMPAIRED
Applying a mobile robot obstacle avoidance system in a travel aid for the blind eliminates several of the shortcomings found in existing devices. Using multiple ultrasonic sensors that face in different directions frees the user from the need to scan the surroundings manually. Furthermore, no additional measurement is required when an obstacle is detected, since its relevant dimensions are determined simultaneously by the multi sensor system. In addition, the obstacle avoidance system can guide the blind traveler toward a target while avoiding obstacles along the path.
The mechanical, electrical and software components, user-machine interface and the prototypes of the two devices are described below. With the development of radar and ultrasonic technologies over the past four decades, a new series of devices, known as Electronic Travel Aids (ETAs), was developed. This seminar introduces two novel ETA that differ from the ETA like C5 laser cane, Mowat 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 thes a few path around detected obstacle. One such algorithm is the Vector Field Histogram (VFH).The VFH method is based on information perceived by an array of ultrasonic sensors (also called Sonars) and a fast statistical analysis of that 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 NAVBELT
Based on our experience with obstacle avoidance for mobile robot, we have developed a new travel aid for the blind, called the Navbelt [Borenstein, 1990; Shoval et al. 1993a]. The Navbelt consists of a belt, a portable computer, and ultrasonic sensors. In this system, the computer processes the signals that arrive from the sensors, and applies the obstacle avoidance algorithm. The resulting signals are relayed to the user by stereophonic headphones, using a stereo imaging technique. The similarity between this approach and the original mobile robot application is illustrated in Fig. 1. The electrical signals which originally guided the robot around obstacles are replaced by acoustic (or tactile) signals.
IMAGE MODE
This mode presents the user with an acoustic panoramic image of the environment by using stereophonic effects: sound signals appear to sweep through the user's head from the right ear to the left. The direction to an obstacle is indicated by the perceived spatial direction of the signal, and the distance is represented by the signal's volume.
The Guidance mode is very similar to the control of a mobile robot. However, this mode of operation requires constantly updated information about the traveler's position. In a mobile robot this information is easily obtained from encoders attached to the vehicle wheels (Odometry). However, the Navbelt is currently not equipped with any positioning feedback device. Possible feedback systems for the Navbelt might comprise of a pedometer and an electronic compass, but it is not clear if this system would be accurate enough. To overcome this problem, we introduced a third operating mode.
THE DIRECTIONAL GUIDANCE MODE
This mode is based on the tele-autonomous mode of operation, which was also originally developed for mobile robots [Borenstein and Koren, 1990]. In this mode the system actively guides the user toward a temporary target, the location of which is determined by the user. The user can prescribe the direction of the temporary target with a joystick; or when a joystick is not used, the target is assumed to be straight ahead of the user. In case an obstacle is detected, the Navbelt guides the user around the object with minimal deviation from the target direction. This mode is particularly efficient for wall following or detecting corners, door ways etc.
AUDITORY IMAGE SIGNALS
The image mode provides the user with a panoramic auditory image of the surroundings. The principle is similar to the operation of a radar system (used in air traffic control, submarines etc.). An imaginary beam travels from the right side of the user to the left through the sectors covered by the Navbelt's sonars (a span of 120o and 5 m radius).
A binaural feedback system invokes the impression of a virtual sound source moving with the beam from the right to the left ear in what we call a sweep. This is done in several discrete steps, corresponding to the discrete virtual direction steps. At each step, the amplitude of the signal is set proportionally to the distance to the object in that virtual direction. If no obstacles are detected by the beam, the virtual sound source is of a low amplitude and barely audible. If, on the other hand, obstacles are present, then the amplitude of the virtual sound source is louder. The amplitude increases for close objects, and decreases if objects are further away.
Figure 4 demonstrates the principle of the image mode. Obstacles are detected by the ultrasonic sensors (Fig 4a), and are projected onto the polar graph (Fig. 4b). Based on the polar graph, the binaural feedback system generates the sweep, which comprises of 12 steps (Fig. 4c). Each step "covers" a sector of 15o, thus the whole sweep covers a panorama of 180o. Each of the eight sectors in the center of the panorama (covering the sectors between 30o and 150o) is directly proportional to the corresponding sensor. The remaining four sectors (two at each side of the panorama) represent sectors which are not covered by the sonars.
The value of these sectors is calculated based on the values of adjoining sectors. For example, if the third sector (representing the first sonar) contains an object, than the first and second sectors are automatically assigned the same value. This way, the sides of the traveler which are not covered by the sensors are blocked, therefore eliminating the possibility of turning into a unchecked area.
IMPLEMENTATION OF AUDITORY GUIDANCE SIGNALS
Implementing the guidance mode in the Navbelt is simpler than the image mode, as the amount of transferred information is far smaller. In the guidance mode the computer provides the user only with the recommended travel speed and direction, based on the obstacle avoidance algorithm.
The travel speed and direction are relayed to the user by a single stereophonic signal. The virtual direction of the signal is the direction the obstacle avoidance system has selected for travel. The pitch and amplitude are proportional to the recommended travel speed. Higher pitch and amplitude attract more human attention, thus the traveler intuitively reduces the walking speed and concentrate on the stereophonic signal. A special low pitch signal (250 Hz) is transmitted when the direction of motion coincides (within +/- 5o) with the required direction.
THE NAVBELT SIMULATOR
To investigate the Navbelt concept under different situations, a simulator was developed. The simulator is based on the same hardware as the Navbelt, and the same acoustic signals that guide the user in the real Navbelt are used in the simulator. The user's response to these signals is relayed to the computer by a joystick. Several maps are stored in the computer's memory, representing different types of environments with different levels of travel complexity.
In the experiments with the simulator, subjects "traveled" through the different maps while listening to the sounds generated by the computer. In the experiments with the image mode, the position of the subject and the location of the target were shown on the computer screen. When subjects "collided" with an obstacle, a verbal message informed the subject about the collision, and no forward travel was permitted. The subject then turned or backed up to continue traveling toward the target. After reaching the target, the full map was superimposed on the traveling path so that the subject's performance during the run could be evaluated.
In the experiment with the guidance mode, only the traveler's simulated position was shown on the screen while the target position was unknown to the subject. This is the equivalent of traveling in an unfamiliar environment, where the traveler depends entirely on the guiding signals from the Navbelt. As with the image mode, when subjects "collided" with an obstacle, a verbal message informed about the collision, and no forward travel was permitted.
EXPERIMENTS WITH THE IMAGE MODE
Experiments with the image mode included three stages. In the first stage subjects listened to different sweeps and drew a map of the environment based on the auditory information. Several combinations of the sweep parameters were examined. The aim was to determine a good combination for perception and fast comprehension of the transmitted signals. Good results from these experiments
were obtained with the following parameters:
Signal transmission time T s varies between 20-40 msec, where 20 msec is used for the longest distance from an object (5 meters) and 40 msec for very close objects (0.5 meter). Space time Tn between signals is kept constant through the whole sweep with Tn = 10 msec. The amplitude A varies inversely with the range reading from the corresponding sonar sector.
Sixteen discrete amplitudes can be selected, where the lowest value represents no threat to the traveler and is not audible at all, while the maximum value represents high risk from that direction. Twelve signals per each sweep (not including the anchoring signals) are sufficient for safe travel, and they require less than 0.5 seconds for the transmission of the whole sweep.
CONCLUSION
A mobile robot obstacle avoidance system has been converted successfully to a navigation aid for the blind. Instead of transmitting electronic signals to the robot motion controllers, the obstacle avoidance system relays information to the user by transmitting stereophonic signals. These signals provide spatial information about the location of objects in space, or guiding information for the recommended travel direction and speed.
The method is implemented in a new travel aid for the blind, the Navbelt. Average traveling speed on the Navbelt simulator in the guidance mode was 0.76 m/sec. The ave0072age traveling speed of blindfolded subjects traveling with the Navbelt prototype was 0.45 m/sec, and 0.6 m/sec along a typical office building corridor. Future developments of the Navbelt will include additional ultrasonic sensors for detecting overhanging obstacles, halls, steps etc.
[attachment=53319]
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 computerized devices based on advanced mobile robotic navigation for obstacle avoidance useful for visually impaired people. This is Bio engineering 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 traveler 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 GuideCane, effectively overcomes this problem. The GuideCane 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 GuideCane detects an obstacle, it steers around it. The user immediately feels this steering action and can follow the Guide Can a new path easily without any conscious effort.
The motion of a blind traveler in an unfamiliar environment is somewhat similar to that of a mobile robot. Both have the physical ability to perform the motion, but are depended on a sensory system to detect obstacles in the surroundings, and to relay the information to the control system (human brain or motion control computer). In both cases, reliable obstacle system is mandatory for fast and safe motion.
MOBILE ROBOTICS TECHNOLOGIES FOR THE VISUALLY IMPAIRED
Applying a mobile robot obstacle avoidance system in a travel aid for the blind eliminates several of the shortcomings found in existing devices. Using multiple ultrasonic sensors that face in different directions frees the user from the need to scan the surroundings manually. Furthermore, no additional measurement is required when an obstacle is detected, since its relevant dimensions are determined simultaneously by the multi sensor system. In addition, the obstacle avoidance system can guide the blind traveler toward a target while avoiding obstacles along the path.
The mechanical, electrical and software components, user-machine interface and the prototypes of the two devices are described below. With the development of radar and ultrasonic technologies over the past four decades, a new series of devices, known as Electronic Travel Aids (ETAs), was developed. This seminar introduces two novel ETA that differ from the ETA like C5 laser cane, Mowat 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 thes a few path around detected obstacle. One such algorithm is the Vector Field Histogram (VFH).The VFH method is based on information perceived by an array of ultrasonic sensors (also called Sonars) and a fast statistical analysis of that 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 NAVBELT
Based on our experience with obstacle avoidance for mobile robot, we have developed a new travel aid for the blind, called the Navbelt [Borenstein, 1990; Shoval et al. 1993a]. The Navbelt consists of a belt, a portable computer, and ultrasonic sensors. In this system, the computer processes the signals that arrive from the sensors, and applies the obstacle avoidance algorithm. The resulting signals are relayed to the user by stereophonic headphones, using a stereo imaging technique. The similarity between this approach and the original mobile robot application is illustrated in Fig. 1. The electrical signals which originally guided the robot around obstacles are replaced by acoustic (or tactile) signals.
IMAGE MODE
This mode presents the user with an acoustic panoramic image of the environment by using stereophonic effects: sound signals appear to sweep through the user's head from the right ear to the left. The direction to an obstacle is indicated by the perceived spatial direction of the signal, and the distance is represented by the signal's volume.
The Guidance mode is very similar to the control of a mobile robot. However, this mode of operation requires constantly updated information about the traveler's position. In a mobile robot this information is easily obtained from encoders attached to the vehicle wheels (Odometry). However, the Navbelt is currently not equipped with any positioning feedback device. Possible feedback systems for the Navbelt might comprise of a pedometer and an electronic compass, but it is not clear if this system would be accurate enough. To overcome this problem, we introduced a third operating mode.
THE DIRECTIONAL GUIDANCE MODE
This mode is based on the tele-autonomous mode of operation, which was also originally developed for mobile robots [Borenstein and Koren, 1990]. In this mode the system actively guides the user toward a temporary target, the location of which is determined by the user. The user can prescribe the direction of the temporary target with a joystick; or when a joystick is not used, the target is assumed to be straight ahead of the user. In case an obstacle is detected, the Navbelt guides the user around the object with minimal deviation from the target direction. This mode is particularly efficient for wall following or detecting corners, door ways etc.
AUDITORY IMAGE SIGNALS
The image mode provides the user with a panoramic auditory image of the surroundings. The principle is similar to the operation of a radar system (used in air traffic control, submarines etc.). An imaginary beam travels from the right side of the user to the left through the sectors covered by the Navbelt's sonars (a span of 120o and 5 m radius).
A binaural feedback system invokes the impression of a virtual sound source moving with the beam from the right to the left ear in what we call a sweep. This is done in several discrete steps, corresponding to the discrete virtual direction steps. At each step, the amplitude of the signal is set proportionally to the distance to the object in that virtual direction. If no obstacles are detected by the beam, the virtual sound source is of a low amplitude and barely audible. If, on the other hand, obstacles are present, then the amplitude of the virtual sound source is louder. The amplitude increases for close objects, and decreases if objects are further away.
Figure 4 demonstrates the principle of the image mode. Obstacles are detected by the ultrasonic sensors (Fig 4a), and are projected onto the polar graph (Fig. 4b). Based on the polar graph, the binaural feedback system generates the sweep, which comprises of 12 steps (Fig. 4c). Each step "covers" a sector of 15o, thus the whole sweep covers a panorama of 180o. Each of the eight sectors in the center of the panorama (covering the sectors between 30o and 150o) is directly proportional to the corresponding sensor. The remaining four sectors (two at each side of the panorama) represent sectors which are not covered by the sonars.
The value of these sectors is calculated based on the values of adjoining sectors. For example, if the third sector (representing the first sonar) contains an object, than the first and second sectors are automatically assigned the same value. This way, the sides of the traveler which are not covered by the sensors are blocked, therefore eliminating the possibility of turning into a unchecked area.
IMPLEMENTATION OF AUDITORY GUIDANCE SIGNALS
Implementing the guidance mode in the Navbelt is simpler than the image mode, as the amount of transferred information is far smaller. In the guidance mode the computer provides the user only with the recommended travel speed and direction, based on the obstacle avoidance algorithm.
The travel speed and direction are relayed to the user by a single stereophonic signal. The virtual direction of the signal is the direction the obstacle avoidance system has selected for travel. The pitch and amplitude are proportional to the recommended travel speed. Higher pitch and amplitude attract more human attention, thus the traveler intuitively reduces the walking speed and concentrate on the stereophonic signal. A special low pitch signal (250 Hz) is transmitted when the direction of motion coincides (within +/- 5o) with the required direction.
THE NAVBELT SIMULATOR
To investigate the Navbelt concept under different situations, a simulator was developed. The simulator is based on the same hardware as the Navbelt, and the same acoustic signals that guide the user in the real Navbelt are used in the simulator. The user's response to these signals is relayed to the computer by a joystick. Several maps are stored in the computer's memory, representing different types of environments with different levels of travel complexity.
In the experiments with the simulator, subjects "traveled" through the different maps while listening to the sounds generated by the computer. In the experiments with the image mode, the position of the subject and the location of the target were shown on the computer screen. When subjects "collided" with an obstacle, a verbal message informed the subject about the collision, and no forward travel was permitted. The subject then turned or backed up to continue traveling toward the target. After reaching the target, the full map was superimposed on the traveling path so that the subject's performance during the run could be evaluated.
In the experiment with the guidance mode, only the traveler's simulated position was shown on the screen while the target position was unknown to the subject. This is the equivalent of traveling in an unfamiliar environment, where the traveler depends entirely on the guiding signals from the Navbelt. As with the image mode, when subjects "collided" with an obstacle, a verbal message informed about the collision, and no forward travel was permitted.
EXPERIMENTS WITH THE IMAGE MODE
Experiments with the image mode included three stages. In the first stage subjects listened to different sweeps and drew a map of the environment based on the auditory information. Several combinations of the sweep parameters were examined. The aim was to determine a good combination for perception and fast comprehension of the transmitted signals. Good results from these experiments
were obtained with the following parameters:
Signal transmission time T s varies between 20-40 msec, where 20 msec is used for the longest distance from an object (5 meters) and 40 msec for very close objects (0.5 meter). Space time Tn between signals is kept constant through the whole sweep with Tn = 10 msec. The amplitude A varies inversely with the range reading from the corresponding sonar sector.
Sixteen discrete amplitudes can be selected, where the lowest value represents no threat to the traveler and is not audible at all, while the maximum value represents high risk from that direction. Twelve signals per each sweep (not including the anchoring signals) are sufficient for safe travel, and they require less than 0.5 seconds for the transmission of the whole sweep.
CONCLUSION
A mobile robot obstacle avoidance system has been converted successfully to a navigation aid for the blind. Instead of transmitting electronic signals to the robot motion controllers, the obstacle avoidance system relays information to the user by transmitting stereophonic signals. These signals provide spatial information about the location of objects in space, or guiding information for the recommended travel direction and speed.
The method is implemented in a new travel aid for the blind, the Navbelt. Average traveling speed on the Navbelt simulator in the guidance mode was 0.76 m/sec. The ave0072age traveling speed of blindfolded subjects traveling with the Navbelt prototype was 0.45 m/sec, and 0.6 m/sec along a typical office building corridor. Future developments of the Navbelt will include additional ultrasonic sensors for detecting overhanging obstacles, halls, steps etc.