Intelligent Robotics Flashcards
Define the condition of holonomy for a mobile robot.
A holonomic robot is a model without non-holonomic constraints, then we can derive the final robot position by the wheels motion. In this case DDOF = DOF.
What is the direct (forward) kinematics for a mobile robot?
The forward kinematics in mobile robotics is the transformation from the joints’ frame to the world’s one. If we are working with a holonomic system with this method we can compute the final position of the robot from the wheels’ rotation, instead if we are working with a non-holonomic system we have to use the velocities. With this approach, the motion problem is seen as a geometrical one.
What are the exteroceptive sensors? List some examples.
The exteroceptive sensors sense the stimuli external to the system.
Examples of this type of sensors are: tactile sensor (like bumpers), active ranging senors (lake laser or sonar) and compass.
List at least 4 sensors for indoor localization of a mobile robot and illustrate how they work.
In indoor application we can use: laser sensors (that emits a laser ray and compute the time of flight to derive the distance between the robot and the obstacles that reflects the ray), bumpers (that are composed by capacitors and can sense if the robot if touching something when they change their shape), gyroscope (that computes the robot inclination deriving it from the angle between the central axis and the fixed ring), and motor encoder (that measures the position and the speed of the wheels, but not their direction).
How many degrees of freedom does a “Synchro Drive” type robot have? Why?
The “Synchro Drive” model is composed by three wheels connected with each other and with two motors: the first controls the orientation of the wheels and the second control their rotation. Then the robot achieves 2 DOF, in fact it can move in 2 directions on the plane but it can’t rotate.
What does “probabilistic localization” mean? Illustrate some probabilistic localization
techniques.
The probabilistic localization is a technique that consists in estimate the current robot’s position by a probability distribution.
For example, if the robot knows a map of the external world, it could perceive which objectes are in front of him and derive a probability distribution of its position. In a second moment, moving around e perceiving other objects, it could refine the previous computed distribution estimating the motion done in the enviroment.
What is the reactive architecture in robotics?
The reactive model is an architecture where the sense-plan-act loop is modified removing the plan phase and there are more than one couple sense-act. This couples are called behaviour and are located in the behavioural layer. Each sense-act frame applies an action based on the external stimuli sensed by the senors or by the controllers’ output.
The advantages are: this approach exploits the modularity, it is cheaper and faster than the classical method (because we skip the plan). The disadvantage is that if more than one couple react to the same stimuli and take different actions which go in contrast, then the robot could break.
What are the proprioceptive sensors? List some examples.
The proprieceptive sensors measure the stimuli produced and perceived within the system and connected with its position or movement.
Examples of proprioceptive sensors are the motor encoders and the gyroscope.
Define: accuracy, precision, repeatability.
Accuracy: in the measurament systems, it is the agreement of the measured value with a given reference standard; in the robotics field, it measures how much close the robot can come to a given point.
Precision: it is the capability to reproduce consecutively the same value in a misuration.
Repeatability: in the measurament systems, it is the capability to reproduce similar values in misuration; in the robotics field, it measures how much close the robot can return back to a previous position.
Explain the software paradigms for mobile robotics.
The 3 paradigm are: hierarchical, reactive and hybrid.
The hierarchical paradigm consists in apply in loop the 3 primitives sense-plan-act. The problems with this method are: it could be a bottleneck in the plan phase and we have to work in a closed world assumption.
The reactive paradigm consists in deploy and apply the sense-act couples in the reactive layer. The problem with this method is that it could fall in a local minima.
The hybrid paradigm combine the reactive layer with a deliberative layer that implements the plan phase.
Explain the forward and the inverse kinematics.
The forward kinematics is the transformation from the joints’ frame to the world’s one. The motion problem is seen as a geometrical one.
The inverse kinematics is the transfomation from the world’s frame to the joints’ one.
What is the SLAM?
The SLAM (Simultaneously Localization And Mapping) amis to solve the robot position w.r.t. a map and at the same time build the map of the surround. This method is based on probabilistic localization based and try to estimate the current position and the map knowing the previous position and the current observations and controllers’ output. It can be implemented using several approaches: belief representation, kalman fiters, particle filters or graph-based represenation.
Define DOF in robotics field.
The Degrees Of Freedom is the number of maximum independent variables used to describe the motion.
1 DOF corresponds to a rigid body that can only translate or rotate in a 1-dimensional path.
2 DOF corresponds to a rigid body that can move on a 2-dimenstional path either translating or rotating.
3 DOF corresponds to a rigid body that can translate along 2 directions and rotate on a plane.
6 DOF corresponds to a rigid body that can move freely in the 3D world.
Explain the wheeled platforms.
There are several models for the locomotion.
We can have 1 fixed and 1 steerable, both without motors or we can add a motor to the fixed one or to the other one.
The Differential Drive model can be built with 2 fixed wheels, each one with a different and independent motor. In this case we have 2 DOF beacause we can achieve the rotation setting different speeds to the wheels. This model has the dynamic stability, but we can achieve the static one too adding a spherical wheel without motor.
With 3 wheels we can have 2 fixed without motor and connected each other and a steerable one with a motor. We can also set up a model with 3 sweedish driven wheels in star configuration.
The Synchronous Drive model can be built with 3 wheels connected between each other and with 2 motors: the first one controls the wheels’ speed and the second one controls their rotation.
Explain the locomotion models for the mobile robot.
The locomotion models are: wheeled locomtion (the robot uses the wheels’ roll to move), sliding (uses the friction), walking (the robot has 2 or more legs), jujmping, crawling, flying.
