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 Knowns

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. The maximum distance measurement is 30 meters
5. ...
6. PICO's velocity and angular velocity can be determined. These are in meters per second and radians per second respectively.
7. ...

The figure on the right shows the location of the laser (distance) measurement points

Tactic

Win!

Master

The Master file is the file which is taking control over everything that happens. Within the master file, there are the executable subfiles and the checking sub files. The checking file "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 checking file "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 program 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

The three possibilities for PICO's position and direction are given in the Figures below. It is either one of these or a combination of two of them.

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).

Detect a corner

The differences between several laser points are used to detect a corner. Five laser points at the side front and five laser points at the side back are in use. When the difference between all front points and back points is larger than some kind of treshold, the corner is detected.
Note that five laser points have been used to robustly detect a corner. When one or two laser points go through a hole in the wall, there should not be a corner detection.
The difference between the two points is taken because else a new corner gets detected whenever a distance is large (for instance right after the turn).
In the figure below, the laser points that are used by PICO are shown. This is the exact moment when the corner to the left is detected.

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 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