ROBOTICS INTRODUCTION
THIS COURSE IS TWO PARTS Mobile Robotics. Locomotion (analogous to manipulation) (Legged and wheeled robots). Navigation and obstacle avoidance algorithms. Robot Vision Sensors and actuators for robots. Industrial Manipulators. Joint space vs. task space. Forward kinematics Inverse kinematics
ROBOTICS Intelligent systems or machines (body and brain) which are able to perform different tasks covering a very wide area of applications: Industry; Manipulators Climbing & Rescue Commercial Cleaning Research Space & Navigation Services: Consumer sales, Security, Civil Transport, & Construction. Medical Services; Surgeries Agriculture & Forestry Hazardous & Energy Mining Undersea Military Personal and Entertainment
THREE MAIN CATEGORIES OF ROBOTS Manipulators (Robotic Arm): Several links are connected through various joints. The base is attached to the ground. Mobile Robots: Can move, interact, and perform a task in an environment. Hybrid Robots: Mobile robot which is provided by an arm.
LOCOMOTION Locomotion is the mechanism that enables the robot to move through its environment. The necessary autonomy of mobile robot depends on the best choice of locomotion that enables it to move freely throughout the surrounding environment. Common locomotion approaches: Wheeled robot (Different types of wheels and configuration) Legged Robot (one, two, four, and six legged robot) Tracked Robot Flying Robot Underwater Robot Ball Robot
WHEELED ROBOT Sojourner was used during pathfinder mission to explore the mars in summer 1997. It was nearly fully tele-operated from earth. However, some on board sensors allowed for obstacle detection. Remote Control Robot Semi-autonomous
HUMANOID ROBOT ASIMO, an acronym for Advanced Step in Innovative MObility, is a humanoid robot designed and developed by Honda.
LEGGED ROBOT Walking robot that is designed to move wood out of the forest. The leg coordination is automated, but navigation is still done by human operator. Semi-autonomous robot example.
TRACKED ROBOT
FLYING ROBOT Unmanned Aerial Vehicle (UAV) drones Mini drones
UNDERWATER ROBOT
SPHERICAL ROBOT (BALL /SPHERO ROBOT)
BALL ROBOT (EXPLAINED) The design is based on heavy weight suspended from the center of the ball. A change in position of the weight along the axis can make the ball move in x and y direction. A semicircular ring pulls itself forward or backward causing an X-Axis movement. The circular ring displaces the semi-circular ring along its plane and causes the weight (added with motor 1 such as a battery) to move in Y-axis and will make the ball move in y direction.
LEGGED LOCOMOTION Legged robot locomotion mechanisms are often inspired by biological systems, which are very successful in moving through a wide area of harsh environments. The main problems are: Mechanical complexity of legs Stability Power consumption. More power is needed than for wheeled if the environment is flat and hard. Energy efficiency depends on the leg and the body mass. Rolling friction of a wheel on a soft ground is the reason why legged robots become better and more efficient. For example, Four legged robot needs at least eight servos to travel around.
WHEELED LOCOMOTION Wheels are a human invention and a very popular locomotion concept in man made vehicles. There is no inspiration in the nature for a wheel, but the human bipedal walking can be approximated as a rolling polygon with sides equal in length d to the span of the step.
ENERGY ISSUE OF LOCOMOTION
ROBOTS MIMICS NATURE
STABILITY OF LEGGED ROBOTS Stability is of course a very important issue of a robot, because it should not overturn. Stability can be divided into: Static stability. Dynamic Stability Static stability means that the robot is stable, with no need of motion at every moment of time. All robots motion can be stopped at every moment in the gait cycle without overturning. Static stability is given, when the center of mass is completely within the support polygon and the polygon s area is greater than zero, therefore static stability requires at least three points of ground contact. ***
STATIC STABILITY OF LEGGED ROBOT One or two-legged robot: Static stability is impossible to achieve in case of one-legged or two legged robots. Four-legged robot: Walking static stable with four legs means that just one leg can be lifted at the same time (lifting more legs will reduce the support polygon to a line), so walking becomes slow. As a result: most robots which are able to walk static stable have six legs.
LEG CONFIGURATION To move a leg forward at least two degrees of freedom are required: One for lifting One for swinging. Most legs have three degrees of freedom; this makes the robot able to travel in rougher terrain and to do more complex maneuvers. However adding degrees of freedom causes also some disadvantages, More joints more servos more power consumption Controlling the robot becomes more complex, because more motors have to be controlled and actuated at the same time.
LEG DESIGN Caterpillar has only a single degree of freedom in each leg, which is oriented longitudinally along the leg. Forward locomotion depends on the hydraulic pressure in the body, which extends the distance between pairs of legs. On the other hand, the human leg has about seven major degrees of freedom.
LEGS COORDINATION The gait is a periodic sequence of lift and release events for each leg. If a robot has k legs the number of possible events N is: N = 2k 1! In case of a bipedal walking machine (k=2) the number of possible events is N=(2k-1)! = (2*2-1)! = 3! = 6 So there are six possible different events, these are 1. Lift left leg 2. Release left leg 3. Lift right leg 4. Release right leg 5. Lift both legs together 6. Release both legs together
CONTROL VS. STABILITY In case of k=6 legs there are already 39916800 possible events More legs in a robot means large number of possible events Thus more complicated legs coordination and control. However, robots with fewer legs have some other problems One of the most complex problems is stability.
ONE LEGGED ROBOT One leg is of course the minimum number of legs which a legged robot can have. Requires just a single point of ground contact; this enables the robot to travel the roughest terrain. Static stability is impossible even when the robot is stationary, because the support polygon is reduced to a single point. Must be dynamically stable, that means that the robot has to actively balance itself either by: Changing its center of gravity Imparting corrective forces. It has to hop all the time.
TWO LEGS ROBOT Dynamic stability issue: Zero Moment Point (ZMP): how to maintain balance by planning footprint positioning. The ZMP is the point where the robot has to base on to keep its balance. When the robot should move forward it has first to compute the ZMP and after that it has to step the appropriate leg exactly to the computed position. ZMP is often described in robotics as the point on the ground where all momentums are equal to zero. ZMP has to be completely within the support polygon. If one leg is in the air, the support polygon is equal to the shape of the foot which is connected with the ground. If both feet are connected with the ground the ZMP can be within the area which is built by the two footprints.
TWO LEGGED ROBOT (HUMANOID ROBOT) Support polygon and the location of the ZMP. Even when standing, must performs continuous correcting contact forces (servoing)
FOUR LEGGED ROBOT Most four legged robots use dynamic stable walking (like nearly all four legged animals), because static stable walking requires at least three points of ground contact. This means that just one leg can be lifted at the same time and so walking becomes slow. In case of dynamic stability the number of ground contact points can vary from zero, when the robot is jumping, to the total number of legs, when the robot is stationary. Fast dynamic walking; balancing challenge is resolved by continuous active shifting of C.G.
STABLE CONFIGURATION When dealing with stability, not all possible configurations are stable.
SIX LEGGED ROBOT Six legged locomotion is the most popular legged locomotion concept because of the ability of static stable walking. Tripod gait is inspired by some insects.
MECHANICS VS. CONTROL CLIMBING ROBOT
CONTROL SCHEME FOR MOBILE ROBOT Semi-autonomous robot relies on human operator in the cognition and localization. Just performs the motion control.
NEXT LECTURE Wheeled Robots Types of wheels Wheels configuration
HOME-WORK QUADRUPED ROBOT Search for at least three different gaits for a 4- legged robot. Explain and compare between these gaits in term of speed, energy efficiency, stability, controllability, and maneuverability. What is the biological counterpart for each gait type?