Selection of Behaviors and Sensors for a Mobile Robot - Research Paper Example

Selection of Behaviours and Sensors for a Mobile Robot Table of Contents Introduction 2 Principle of Operation 2 Description of Behaviours 5 Specifications of Sensors for Behaviours 6 Sensor Inputs 8 Robot Operation 9 Commercially Available Sensors 10 Conclusion 19 Works Cited 21 Introduction A design of the behaviours of a mobile robot, which delivers sandwiches to people in an open meeting room, has been prepared. A robotics conference is underway and delegates of the conference have gathered in the conference room for a social event and a buffet meal. The room is 10 metres wide and 20 metres long. There are 10 tables spread around the room, where drinks and glasses are placed. Along the longer side of the room is a long table with catering staff behind them ready to give trays of sandwiches to robots. There are 5 robots. Each robot approaches guests to a reasonable distance and waits for them to take a sandwich. Each robot travels around the room to make sure that all guests are served. While travelling, they avoid collisions with guests, tables, or the walls of the room. When the tray is empty, each robot returns to the catering table and collects a full tray from the catering staff. Principle of Operation The room layout has been illustrated in figure 1. To simplify the navigation of robots, the room has been divided into 5 zones and each zone has been divided into smaller grids. A robot travels within its zone. In each zone, a base station has been set near the catering table. The base station serves to help the robot navigate within its zone, refill trays, and as a point of return in case of any malfunction. Each robot is stationed at its base station. When the event starts, catering staff load a tray full of sandwiches on the robot. The robot senses a full tray and then travels around the room, stopping near guests allowing them to pick sandwiches. While travelling, the robot should be able to distinguish stationary guests from moving guests, tables, walls and other objects. The robot should be able to maintain steady motion and detect collisions. When the robot is offering sandwiches to guests, it should be able to sense guests picking sandwiches and wait for them to have completed picking the sandwich. The robot should continue to travel within its zone and continue to offer sandwiches. When the tray is empty, the robot should be able to sense it and return to base station for a new tray. The process is repeated until the event is over. When the event is over, the empty tray is not refilled. The robot should remain in its base station and turn off after some time. The following behaviours are necessary for the robot to accomplish the task: 1) Navigation; 2) Detection and distinction between guests, tables, and other objects; 3) Maintenance of steady motion and detection of collisions; 4) Detection of guests picking up sandwiches; and 5) Detection of empty and loaded trays. Figure 1. Room Layout Figure 2. Robot (e-Motion, 2004) Figure 3. Robot with Sensors Description of Behaviours Each robot is stationed at its base station. Under normal circumstances, this would mean that the tray is empty. When a full tray is loaded by the catering staff, the robot should be able to detect it, so that it is able to offer sandwiches to guests. Also, when the tray is empty, the robot should be able to detect it. On being loaded with a full tray, the robot should be ready to navigate. To do so, the robot should be able to sense the environment. This includes detection of stationary objects, such as guests, tables, walls etc. and mobile objects, such as guests. On detection of mobile objects, the robot should be able to detect acceleration and direction of movement. When the environment has been sensed, the robot should be able to navigate to the nearest group of guests to offer sandwiches. The path of travel should avoid objects, such as walls, and tables. The pre fed zone should be used as a map with the base station as reference, and the entire zone covered. While travelling, it should avoid colliding with objects, particularly accelerating objects. When the robot travels to a group of guests and offers sandwiches, it should be able to detect guests picking up sandwiches and allow the completion of the activity. When all the sandwiches on the tray have been picked up, the robot should be able to detect the empty tray, so that it can return to base and have the tray refilled. Specifications of Sensors for Behaviours Localization Sensor: Sensors are required for localization, and continuously positioning the robot with respect to a pre defined map. The room is 10 metres wide and 20 metres long. It has been divided into five zones, 2 metres wide and 4 metres long, one for each robot. Landmarks have been attached to the ceiling within the zones. Infrared sensors are required to measure the position the robot several times each second (10/sec approximately). Infrared ray projection and image processing capabilities are required. The sensor should be small (less than 5 cm x 5 cm x 5 cm) and has to be mounted on top of the robot. Travel range for the robot is within an area of 3 metres x 5 metres. The ceiling height is less than 5 metres. Power consumption should be low (less than 2.5W approximately). Environment Sensor: Sensors are required for ranging and imaging. The travel zone of the robot is full of tables, people, and other objects. The area within each zone is less than 3 metres wide and 5 metres long. The sensor should be able to sense within this area in all directions. High speed laser scanners are required to create profiles of objects and measure distances. The power consumption should be low (less than 2.5W approximately). The sensor has to be mounted on top of the robot and should be small (less than 10 cm x 10 cm x 10 cm). Accelerometer: An Accelerometer is required to measure motion and sense shocks. A 2 axis accelerometer with analogue output is required. The power consumption should be low (less than 2.5W approximately). The size should be small (less than 5 cm x 5 cm x 5 cm) and the sensor has to be mounted at the bottom of the robot. The load to be driven is less than 10 kg. It should be rated at least 2g. Vision Sensor: A vision sensor; specialized photoelectric sensor, is required to detect the presence of guests within an area while picking up sandwiches. The sensor has to be placed above the sandwich tray. The sensing requirement is within 50 cm x 50 cm x 50 cm. The sensor is required to identify human form, specifically the hand while picking up sandwiches. The power consumption should be low (less than 2.5W approximately). The size should be small (less than 15 cm x 15 cm x 15 cm). The lens should be adjustable within the specified range. There should be infrared blocking capability, and the sensor should be able to detect colours and lines in real time. Force Sensor: A force sensor is required to detect empty or loaded trays. The sensor has to be placed on a platform below the position of the tray. The weight of the tray with sandwiches is 2 kilograms approximately. Loads on a platform could be measured by the use of resistances. The power consumption should be low (less than 2.5W approximately) and the size should be small (less than 5 cm x 5 cm x 5 cm). Sensor Inputs The environmental sensor is a high speed laser scanner that scans the environment surrounding the robot. The scanning system associated with the sensor should be able to differentiate humans from other objects, such as tables, etc. Once such a distinction has been made, the system should be able to measure the distance to the nearest group of humans. The input from the scanning system is differentiation of humans from objects and distance to them. Some pre programming is required to train the system to recognize human profiles. The location sensory system comprises of infra red projector that emits rays to stationary landmarks on the ceiling several times a second generating a path of travel from its base station. The system has a pre fed map of the zone. As the robot navigates within the zone, the sensory system tracks the movement on the map. The accelerator is required to measure motion and balance. It is required to maintain a steady motion and detect shocks. The input from the sensor is acceleration along two axes. The vision sensor is a specialized photoelectric sensor that is pre programmed to recognize human forms, especially hands picking sandwiches. The output from the system is one of two states. The on state, where a human and hand has been detected picking up a sandwich, and an off state, where there is no hand or human within the sensing area. The force sensor is used to detect loaded or empty trays. The input from the sensor is one of two states. The on state represents a loaded tray and the off state represents an empty tray. Robot Operation The robot is stationed at the base station within its zone along the catering table. The input from the force sensing system is off indicating that the tray is empty. When catering staff loads a tray on the robot, the input from the force sensor turns on, indicating that the robot is ready to go. The input from the vision system is off indicating that there is no human presence within the tray area and the robot is free to move. When the input from the vision system is off, the input from the environmental sensing system is the direction of the nearest stationary human or group of humans. The localization system has a pre fed map of the zone and calculates the ideal path to the target, avoiding known obstacles, such as tables. As the robot proceeds, a trail from the base station is generated by the localization system and the environmental sensing system continues to monitor the environment for new obstacles, such as moving people. The accelerator system maintains steady motion. If the vision system detects a new obstacle, such as a moving person it stops until the obstacle has moved away. Also, the robot stops when a collision is detected. The robot is pre programmed to stop 0.5 metres from the target. It is pre programmed to stop for a minute or as long as the input from the vision system is on. After the vision system has turned off, the robot waits for another minute. When the robot is stopped, the environmental system senses the next nearest human or group as the next target and the process is continued until the input from the force sensor is off. When the input from the force sensor is off, the robot waits for a minute, and the robot is pre programmed to find the ideal path to its base station for a new tray. Commercially Available Sensors The sensors required for the task have been listed and commercially available sensors have been illustrated in table 1. Table 1: Commercially Available Sensors Sensor Manufacturer, Part No, Details Cost Power Consumption Localization Hagisonic StarGazer Robot Localization System Product code : RB-Hag-01 Hardware interface: UART (TTL 3.3V), 115,200bps Size: 50x50x28 mm Communication Protocol: User protocol based on ASCII code Measurement Time: 20 times/sec Localization Range (per a Landmark): 2.5~5m in diameter (for ceiling height 2~6m) Repetitive Precision: 2cm Heading Angle Resolution: 10 degree Landmark Types and application: HLD1-3: 2.9 m = Height = 4.5 m (Robot Shop, 2008) US $1,522.99 5V: 300mA, 12V: 70mA Environmental Hokuyo URG-04LX Scanning Laser Rangefinder Product code : RB-Hok-01 Class 1 infrared laser scanner (0.8 mW or less) Light weight (160g) Range is 20mm to 4000mm Ultra compact size (50 x 50 x 70mm) +/- 10mm accuracy 100 msec scanning time 1-year warranty (Robot Shop, 2008) US $2,369.00 Low power consumption (2.5 Watts) allows for longer battery life in robotic application. 500mA at 5V. Acceleration Dimension Engineering Buffered ±5g Dual Axis Accelerometer (ADXL320) Product code : RB-Dim-01 Dual axis ±5g sensing 312mV/g sensitivity at 5VDC 500Hz bandwidth Accurately drives up to a 3k? load Based on the Analog Devices ADXL320 Dual Axis ±5g Analog Interface Reverse voltage, 14v overvoltage and output short protection Dimensions: 10x18mm Weight: 0.9g (Robot Shop, 2008) US $23.64 Operating voltage 3-5V Draws less than 2mA Vision Mindsensors NXTCam-v2 Vision Sensor Product code : RB-Min-01 Vision sensor for NXT tracks colors or lines in real-time I2C interface with Lego Mindstorms NXT connector USB "Mini B" interface for optional PC operation Perfect for education and experimenting with robotic vision The Mindsensors NXTCam-v2 vision subsystem allows users to define their object colors and track objects. Track up to 8 objects simultaneously. The object shapes could be boxes or lines. Reporting coordinates for all the objects it finds to the NXT. This is an excellent device for innovative educational courses, covering robotic vision. NXTCam can also be used as a color sensor, Roboball sensor, IR-Seeker, etc. Features: Connects to NXT on a sensor port Connects to computer using USB interface (USB Cable sold seperately, RB-Spa-47) Tracks line or up to 8 objects (with 8 different user defined colors) at 30fps Adjustable lens focus Lens with built in infrared blocking filter Provides real-time tracking statistics to NXT PC not needed for autonomous operation on NXT Supported environments: NXT-G, RobotC, LeJOS, NXC Enclosed Design Note: Using NXTCam requires fair amount of programming expertise and analytical skills. (Robot Shop, 2008) US $158.74 42 mA (max) at 4.7V Force 4" FlexiForce 0-25 lbs. Resistive Force Sensor Item #: S-20-1000-FS25LB-4inch A versatile, durable piezoresistive force sensor that can be made in a variety of shapes and sizes A piezoresistive sensing device in which resistance is inversely proportional to applied force A customizable, economical force measurement tool that is easily integrated into OEM products A patented, ultra-thin (0.008"), flexible printed circuit that senses contact force A force and load sensor that is available in three different force ranges, suiting a variety of applications for research and product development/testing. Thickness 0.008" (.208mm) Length 8" (203mm) 6" (152mm) 4" (102mm) 2" (51mm) Width 0.55" (14mm) Sensing Area 0.375" diameter (9.53mm) Connector 3-pin male square pin Thickness 0.008" (.208mm) (Tekscan, 2009) US $16.75 25mA (max) at 5V Conclusion Behaviours for the robot to accomplish the task of offering sandwiches are: navigation; detection and distinction between guests, tables, and other objects; maintenance of steady motion and detection of collisions; detection of guests picking up sandwiches; and detection of empty and loaded trays. Location, environmental, acceleration, force and vision sensors are required for achieving the behaviours. Commercially available sensors have been identified. Works Cited e-Motion, "notre_koala." e-Motion. 2004. Inria and the LIG Laboratory. 25 Mar 2009 . Robot Shop. "Robot Parts." Domestic and Professional Robots, Robot Parts, Robot Kits, Robot Repair. 2008. Robot Shop. 25 Mar 2009 . Society of Robots. "How to Build a Robot Tutorial." How to Build a Robot Tutorial. 2009. Society of Robots. 25 Mar 2009 . Strain Measurement Devices. "Load Cell and Force Sensors." Strain Measurement Devices. 2009. Strain Measurement Devices. 25 Mar 2009 . Tekscan. "FlexiForce® Force Sensors." Tekscan. 2009. Tekscan. 25 Mar 2009 . Read More