Embedded Motion Control 2014 Group 8

This is the WIKI of group #8. Group members Name Student ID Email Harm van Deursen 0707393 h.j.b.v.deursen@student.tue.nl Lex Hoefsloot 0718252 a.v.hoefsloot@student.tue.nl Teun Melief 0656886 t.j.melief@student.tue.nl Robin Smit 0756271 r.smit@student.tue.nl Paul Verhoeckx 0663727 p.b.verhoeckx@student.tue.nl PICO information 1. 1080 laser points for distance measurement 2. approximately 250 degrees of measurement direction 3. The datapoint at the left (930), front (540) and right (150) 4. PICO's input for the velocity and angular velocity are in respectively m/s and rad/s. The figure on the right shows the location of the laser (distance) measurement points Project structure Below, the structure of the program is explained. Master The Master file is the file which is taking control over everything that happens. Within the master file, there are the options that should be checked and actions that should be performed. The checking action "Detection" is constantly sending (with a frequency of 20 Hz) information to the master. The information which is sent is whether there is; nothing special, a corner, a corridor, a T-junction, a plus-crossing or a dead end. The decision action "Strategy" is receiving information from the master. This information is about whether something is detected or not and what is detected (by "Detection"). Then within "Strategy" it is determined whether there is an arrow or not. With this information, a desired direction is replied to the master. Next to the checking sub files there are two executers. Note that either one of both can be executed. The drive block is called when "Strategy" does not give any input to the master. When "Strategy" does however, "Prefered turn" is the action to be executed. The figure below gives a visual representation of the interaction within the system. For extra clearity, the movies below shows the nodes in use while PICO is running. Driving straight For the PICO to be able to drive straight to the corridors a “drive straight” component is implemented. This is used when no walls are critically close and no corners are detected yet. To do so first of all the ranges of N odd points, which are equally distributed over the frontal view of the robot, are evaluated. When any of these ranges is less than a certain treshold, the angle with the nearest wall is calculated. Therefor the smallest range of the set is selected, and it is assumed this represents the distance perpendicular to the wall. This is depicted in the left situation in the picture below where N=7, the use of the dashed lines is explained later. Now the angle θ is calculated with the use of the smallest range and the range straight ahead which are presented in red. When this angle is known the angular velocity is controlled with a PD controller which forces θ to zero. This basic controller equals: ω = P*θ + D*θ’. To calculate the time derivative of θ, a first order linear differential equation is used. However if the nearest wall is not the wall PICO is directed to this approach would fail. This situation is shown in the right picture below, where the far left (orange) range is the smallest of the set. Now this range is compared with the dashed (green) range which is pointing slightly backwards. When this dashed range is smaller it is clear PICO is directed to the other wall. Now the smallest range on the other side is used to calculate θ, as shown with the red arrows. Drive safely To drive safe is the main task of this project. For this reason it is always checked (if just driving forward, in a turn, etc.) whether or not a wall is too close. There are four possible cases of too close: At the front, left (laserpoints 540 till 680) a wall is detected At the front, right (laserpoints 400 till 540) a wall is detected At the left side (laserpoints 680 till 1080) a wall is detected At the right side (laserpoints 1 till 400) a wall is detected In the first two cases, the robot drives backwards and turns to the right (in the first case) or to the left (in the second). In the second two cases the robot keeps driving but steers to the right (in the third case) or to the left (fourth case). Corner detection The differences between several laser points are used to detect openings. On both sides five laser points diagonally to the front and diagonally to the rear are used, as well as five laser points straight ahead. When the difference between all the askew frontal and rear points are larger than some threshold, an opening is detected. Note that five laser points are used for robustness. If one or two laser points would go through a hole in the wall, no opening should be detected. The difference between the two points is taken in order to use relative distances instead of absolute ones. Otherwise a new corner could be detected whenever a distance is large, for example in a large open field. If an opening is detected there are four possible situations: There is a crossing; There is a T-junction; There is an exit into a new corridor; There is a single corner. Ideally a crossing is detected as in the left figure below: at both sides an opening is detected as well as the opening straight ahead. However, if PICO arrives in a direction not exactly parallel to the wall one side opening is detected first, as will be the case in practical situations. Therefore, if a side opening is detected, a new set of laser point (the green area in the right figure below) checks for an opening at the other side too. If so, a crossing is found. Detect a corridor Detect a T-junction Detecting a T-junction is something that automatically is 'asked' when a corner is detected. If a corner is detected at one side, laser points even more in the front will be used to check whether there is a corner at the other side as well. This is visualized in the figures below. In the left figure, a corner to the left is detected. Immidiately PICO compares the light grey laser points at the right with the right lower laser points. If that distance is bigger than a certain treshold, the 'corner detected' changes into 'T-junction detected'. Detect a crossing Detect a dead end The pico does not only continously checks for corners, but keeps track whether the road ahead is free. If there is no corner spotted and a wall is detected ahead, this means the pico has run into a dead end. This is also send back to the masterfile, so that a u-turn can be made instead of letting the drive safe modus inefficiently turn the pico around. Strategy If a single corner to the left or to the right is found without any other options, these corners should obviously be taken. But if, in case of a corridor, T-junction or crossing,where multiple options are available, a choice has to be made whether a corner should be taken or not. If an arrow is detected which points to a direction which is not an option for the pico (if there is no corner found in that direction), the arrow is neglected. This is for driving more robustly if the corner detection misses any corners. If an arrow is found which points to a direction in which a corner is found, the pico always follows the arrow, regardless of any previous choices made or any other strategic considerations. If no corner if found, the pico always prefers taking corners to the right and avoids taking corners to the left as much as possible. This essentially makes the pico a wall follower, with a preference to the right. Previous corners taken are not saved of stored anywhere since the have no influence on the decions in the future. Take the corner Once there is decided that a corner or u-turn should be taken, a subfile is called from the master file. The input for this subfile is wheter the corner is to the right, to the left or a u-turn. In case of a u-turn, the pico simply spins approximately 180 degrees and continues driving in the opposite direction. In case of a corner to the left or right, the subfile performes 2 actions. First, the forward and angular velocities are set to a fixed value and the pico makes the corner for a fixed amount of time. Next, the forward velocity is set to a value without any angular or side velocity and the pico drives forward for a fixed amount of time, without checking for any new corners. This second action is performed to prevent the detection to detect a new corner immediately after finished the first corner, in case it is taken to short or incorrect. While performing these actions, the lasers keep updating their values. Unlike in the previous section of driving safe, the lasers are now divided into two subsections: left and right. If something is spotted on the left while taking the corner, a sideways velocity is added to the right. The other way around applies when a wall is found to close to the right. The forward and angular velocity are not altered when something is detected. Since makeing the corner is performed for a fixed amount of time, altering the forward or side velocity when something is detected whould result in a corner which is to short. For the driving forward after making the corner, the same safety applies as for the normal safe driving. Arrow detection These are the steps taken by 'arrowDetection': Converting ROS image to an OpenCV image. Converting the RGB OpenCV image to an HSV image. Thresholding the HSV image in order to create a binary image of environment in which only bright right objects are 'white' and the rest is 'black'. Dilate the image to remove any black spots in white surfaces. Erode the image to create sharper edges Preform template matching: matching images of left and right arrows to check wether they are present in the picture. Only if the similarity between the template and the camera footage is above a certain threshold, the template is considered 'found' in the image. Matching of the two types of arrows is compared. The one with most similarity to the arrow in the camera feed is chosen. Depending on the result, either 0 (no arrow), 1 (left arrow) or 2 (right arrow) is being sent to the strategy of pico. Algorithm to solve the maze In order to complete the maze as fast as possible the program uses a fixed strategy. When the robot detects a situation where it can continue in multiple directions it chooses a preferable one. This decision is made based on two parameters, namely which options it detects and whether or not an arrow is observed. When an arrow is detected in a direction which is a subset of the detected options this will be the preferred new direction. In the case the robot observes an arrow in a direction which is not part of the found options, the arrow is ignored and a direction is chosen based on the rules explained below. When a crossing is observed without the detection of an arrow, the program chooses the new direction according to a fixed sequence. If possible it chooses to go right, otherwise to go straight. This ensures that every corridor of the maze is evaluated before returning to the same crossing. Tests During each test session, several things are tested seperately and observations are done. This chapter is about the logging of all the information. First test [15/05/2014] The first goal was to survive the corridor test. This means any corner, left or right, should be detected and taken without any collosion. There were two main tactics to be tested; Global tactic (inserted in both programs): - The corner can be detected by either laser point #150 or #930. - Safety (not hitting the wall) is inserted for the measurement points 150 - 250, 400 - 540, 540 - 680 and 820 - 970. first tactic: 1. The distance in front is measured and saved when a corner is detected. 2. Than PICO starts rotating until the distance on the side where the corner has not been measured is equal to the distance that was previously in front 3. PICO drives sidewards until the distance is 30 centimeters less 4. pico drives straight ahead again. The corner is taken Second tactic: 1. The corner is measured but PICO keeps on driving straight ahead and the timer starts 2. The end of the corner is detected and the timer stops 3. PICO drives backwards for half of the time the timer has measured 4. PICO drives sidewards through the corner 5. PICO turns to get back in its neutral position Observations; - All measurement points should be used for safety to ensure safety - The big mess should be cleaned and divided into seperate files which will be included into the master file - One point to measure a corner is not robust. This should be done by the use of more points. However, the second tactic seems to work quite okay and will thus be used for the corridor competition Corridor test [16/05/2014] Unfortunately there was not enough time to implement the observations in the code. The second method is used and led to a time to pass the corridor in 32 seconds. second test [21/05/2014] In the second test the new safety driving, the new corner detection and the straight driving have been tested. The method to detect a corner was adjusted. Where earlier corners were detected with only one laser point, the new corner detection got a lift. They are detected via the subtraction of five laser points at the side and five laser points at the side a bit more backwards. Parameters such as the difference and the position of these laser points which are used are tuned within this meeting. To get the exactly desired position where a corner should be detected, PICO is placed at the place where the corner should be detected. Two points that differ half a meter in distance are used as the points for measuring a corner. For robustness this is extended to the five closest measurement points. The safe driving is used in any of the testing cases. It is working very properly. The only thing is that the safety margin sometimes seems to be less than .3 meters. The straight driving has also been tested. Whereas it works perfectly in the simulations, it worked properly one out of ten times in the tests. This is given the highest priority to get right for the next test session. Third test [05/06/2014] Fourth test Fifth test C++ coding Master As depicted in the file above, the master file is the file which activates other files and which the other files answer to, but doesn't perform any actions itself. This file keeps looping the entire time, as long as all the hardware and software keep working correct. In every loop, the first thing the master node does is activiting the file which checks for corners or dead ends. This file answers with an integer, which stands for a corner to the right, left, dead end, corridor, T-junction or crossing. Also every loop a file for the arrow detection is called upon, which checks for arrows and stores the results. This file returns a integer, which stands for an arrow to the left, to the right or no arrow found. If one or more corners are found, a strategic file is called. This strategic files takes 2 integers as input from the master file: if an arrow if found (and which side it is on) and what options it has: corner to the right, left, etc. This strategic file returns an integer. This integers says which action should be performed: making a corner to the left, to the right or driving straight ahead. If a corner or u-turn should be made, the master file calls a file is which preformes this action. If no corner is found, or it should not be taken, the master file calls the drive safe file, which is responsible for the straight and safe driving of the pico. Check corner This is the first file called every iteration from the master file. It has no inputs and checks for corners as described above. It returns an integer to the master file with information on what corner type is found: T-junction, crossing etc. Arrow detection Arrow detection is built into a different node than the rest of pico's controllers. This is to make sure that the image processing is not interfering with the pico driving controllers. The master node can subscribe to the image processing node on the topic 'arrowDetection'. ArrowDetection is posting '0' if no arrow is found, 1 if a left arrow is found and 2 if a right arrow is found. When the arrow detection node is started, it begins processing the camera topic of pico. Strategy The strategy file is called by the master file in case a corner is detected. It takes two integers as input; one for the type of corner and one for the arrow detection. It returns an integer to the master file with an option to make the corner to the right, left or drive straight ahead. Make corner This file is called by the master in case a corner has to be taken. It takes an integer with the option for a corner to the right, left or u-turn. The file keeps calling the safety file twice (one for the left side of the pico and one of the right side) to check if the pico is at a safe distance of the walls. As long as the safety file returns true, this files makes the corner for a fixed amount of time. If the safety file returns false, this file adds a side velocity to the pico away from the wall. The file gives no output back the the masterfile Safety This file is called by both the drive file (see below) and the make corner file. It takes 2 integers and a double as input; first a number for the laser where the file should start checking the distance, a number for the laser where the file should stop checking the distance and a double which represents the threshold for which the pico is safe or not. By including the start and stop number for which laser should be checked, this file allows the other files to only check certain areas relative to the pico (left, right, ahead, etc). The file returns a boolean saying if the pico is safe or not. Drive This file is called by the master in case the pico should just drive straight. It takes no input and gives no input back to the master file. In the file, first the laser values are read and, when needed, action is taken to prevent collision. When nothing is detected below a certain threshold, the pico can focus on driving straight. Thesefore a new file is called. Driving straight This file is called from the drive file and takes no input nor returns an output. It uses the PD controller to keep the pico straight.

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