Embedded Motion Control 2019 Group 2

Group members

• 1. Bob Clephas | 1271431
• 2. Tom van de laar | 1265938
• 3. Job Meijer | 1268155
• 4. Marcel van Wensveen | 1253085
• 5. Anish Kumar Govada | 1348701

Intro

This project is a part of the Embedded Motion Control course in which a particular software architecture and behaviour is designed for the PICO robot to execute tasks autonomously keeping in mind the various constraints. It is comprised of the escape room challenge and the hospital challenge. The goal of the escape room challenge is to exit the room from any given initial position of the PICO inside the room in minimum time. The goal of the hospital challenge is to visit an unknown number of cabinets in a specified order placed in different rooms in minimum time. A very generic software structure was implemented so as to tackle both the challenges. The design requirements, specifications, software architecture, program flow and the results of the two challenges are shown in the following sections.

Design document

To complete the two assignments for the course “Embedded motion control” specific software must be written. In this design document the global architecture of the software is explained, and the given constraints and hardware is listed. This document is a first draft and will be updated during the project. The first version can be found here.

Requirements and specifications

The requirements and related specifications are listed in the following table. The listed specifications are required for the final assignment and the escape room challenge.

Requirements	Specifications
Accomplish predefined high-level tasks	1. Find the exit (Escape room challenge) 2. Reach a predefined cabinet (Hospital Competition)
Knowledge of the environment	1. Location of walls (via corner points) 2. Location of the doors (via corner points) 3. Location of the cabinets (via corner points) 4. Location of static objects (via corner points) 5. Location of dynamic objects (via corner points) 6. Map at 2D level 7. Accuracy of 0.1 meter
Knowing where the robot is in the environment	1. Know the location at 2D level 2. XY with < 0.1 meter accuracy 3. Orientation (alpha) with <10 degree accuracy
Being able to move	1. Max. 0.5 [m/s] translational speed 2. Max 1.2 [rad/sec] rotational speed 3. Able to reach the desired position with <0.1 meter accuracy 4. Able to reach the desired orientation with <0.1 radians accuracy
Do not bump into the wall	1. Keep a circle with radius >0.3 meter free of obstacles around the robot
Standing still	1. It is not allowed to stand still for longer than 30 seconds
Finish as fast as possible	1. Within 5 minutes (Escape room challenge) 2. Within 10 minutes (Hospital Competition)
Coding language	1. Only allowed to write code in C++ coding language 2. GIT version control must be used

Components and functions

The components and their functions are split in software components and hardware components.

Software components

Software block	General functionality
World model	1. Storing all the relevant data (Map / tasks / position/ etc.) 2. Data communication between the other components (All data goes through the world model)
Task manager	1. Set operation modes of other blocks depending on the current status of the blocks and high level tasks
Perceptor	1. Reading sensor data 2. Identifying walls and objects based on laser data and create local map 3. Fit local map onto global map (Hospital Competition) 4. Locate robot on local map (Escape room challenge) 5. Locate robot on global map (Hospital Competition) 6. Keep local map aligned with global map (Hospital Competition)
Path planner	1. Create a path from the combined map, current position and the desired position 2. Check if path is free and plan new path if current path is blocked 3. Keep track of open and closed doors
Drive controller	1. Actuates the robot such that it arrives at the desired location (keep speed and acceleration in mind) 2. Check if the desired direction is safe to drive to (based on laser data obtained from perceptor, not based on the map)

Hardware components and their general functionalities

Hardware module	General functionality
PICO Robotic platform - Jazz telepresence robot	General framework with all the hardware. This framework will allow to execute the assignments
Sensors: - Laser range finder - Wheel encoders - 170⁰ wide angle camera	Scan environment and detect objects Determine the traveled distance by the wheels Can be used for vision system (object detection for example)
Actuators: - Holonomic base (omni-wheels) - Pan-tilt unit for head	Allows the robot to move on the ground Can be used to move the head with the display and camera
Computer - Intel I7 processor - OS: Ubuntu 16.04 (64-Bit) - ROS with own software layer	Perform computations Software that allows execution of programs Allows to easily make connections between software and hardware

Environment

The environments for both assignments will meet the following specifications:

Escape room challenge
- Rectangular room, unknown dimensions. One opening with a corridor.
- Starting point and orientation is random, but equal for all groups.
- Opening will be perpendicular to the room.
- Far end of the corridor will be open.
- Wall will not be perfectly straight, walls of the corridor will not be perfectly parallel.
- Finish line is at least 3 meters in the corridor, walls of the corridor will be a little bit longer.

Final challenge
- Walls will be perpendicular to each other
- Global map is provided before competition
- Location of cabinets is provided in global map
- Static elements, not showed in global map, will be in the area
- Dynamic (moving) elements will be in the area
- Objects can have a random orientation
- Multiple rooms with doors
- Doors are time-varying opening an closing
- list of "To-be-visited" cabinets is provided just before competition

General software architecture and interface

TODO: Anish

The overall software is split in several building blocks such as the Task manager, World model, Perceptor, Path planner and Drive controller as shown in the figure below :

Data flow

Block	Data	Transition from	Transition to	Block	Data	Transition from	Transition to
Perceptor	Lazer range finder data	LRF Sensor input	Perceptor	Path planner	Desired destination	World model	Path planner
	Odometry data	ODO Sensor input	Perceptor		Current position	World model	Path planner
	Json file - Global Map and location of cabinets	File read	Perceptor		Combined map	World model	Path planner
	Perceptor block modes	World model	Perceptor		Path planner block mode	World model	Path planner
	Local map	World model	Perceptor		Path planner block status	Path planner	World model
	Global map	World model	Perceptor		Next node	Path planner	World model
	Current position	World model	Perceptor		Path from Dijkstra algorithm	Path planner	World model
	Zero position	World model	Perceptor	Drive controller	Desired location	World model	Drive controller
	Global map	Perceptor	World model		Current location	World model	Drive controller
	Perceptor block status	Perceptor	World model		Close proximity region	World model	Drive controller
	Local map	Perceptor	World model		Drive controller block mode	World model	Drive controller
	Combined map	Perceptor	World model		Drive controller block status	Drive controller	World model
	Zero position	Perceptor	World model		Motor set point	Drive controller	World model
	Current position	Perceptor	World model
	Close proximity region	Perceptor	World model
Task manager	User input cabinet list	User	Task manager
	Block status	World model	Task manager
	High level tasks	World model	Task manager
	Block modes	Task manager	World model
	Updated high level tasks	Task manager	World model

Overall program flow

Figure 2: Overall program structure with phases

The overall program is divided in 5 phases. During a phase all actions lead to one specific goal. When the goal is reached, a transition is made towards a new phase. Within a phase it is possible to have multiple cases. Each iteration of the program it is evaluated to what phase and case the program should move. It is also possible to stay in a specific phase and case for longer than one program iteration, however, in most situations this is not needed. Every case has a specific block mode for each software block and the transitions between cases and phases is based on the blockstatusses of all blocks.

Phases flowchart

In figure 2 the overall structure with the phases is shown. The different phases have the following goals:

Phase	Goal
Init	Initialise all blocks
Fitting	Fit the local map onto the global map and determine the location of the robot onto the global map
Relocate	Move the robot to a desired cabinet. This includes: - Planning a path - Driving the robot along the path - Check if path is blocked - Measure environment and update map - Update location of the robot
Cabinet_action	Perform required interactions with the cabinet
Error	Bring the robot to a safe state, output an error to the user and exit the program

Init phase

The init phase focuses on the initialisation of the program. This phase has one case and the flowchart of this phase is shown in figure 3.

Figure 3: Init phase

During the init phase the following actions are executed:

Block	Actions
Taks manager	- Init blockmodes of init values for all blocks - Set blockstatusses to init values for all blocks - Read and store high level tasks - Read taskplanner behavior from file and store
Perceptor	- Read Json file and create map - Generate global map - Set zero coordinates - Create cabinets
Path planner	- Create nodes (around doors, middle of the room, in front of cabinets) - Link nodes
Drive controller	- Init PID controllers

Fitting phase

Figure 4: Fit phase

In the fitting phase the goal is to locate the robot relative to the given global map. This fitting is done in the perceptor by checking the laserdata, creating a local map and try to find a best fit between the local and global map. If this fit is successful the location of the robot is known and all new laser information can be used to update the location of the robot.

Case	Actions
Case 1 - Fit	- Obtain laser data - Create local map - Try to fit local map onto global map
Case 2 - Change desired location	- set new desired orientation to (current orientation + predefined angle)
Case 3 - Drive	- drive robot to new desired location/orientation
Case 4 - Change desired location	- Set new desired location to the middle of the room

Relocate phase

Figure 5: Relocate phase

In the "Relocate" phase the goal is to drive the robot to the next cabinet. The driving involves the path planning, actuating the drivetrain of the robot and avoiding obstacles. During the driving the perceptor keeps updating the world map and keeps adding objects to the map is necessary. Also the fitting will be improved once more laserdata is obtained.

In figure 5 the overall flowchart is shown of the relocate phase. This phase contains the following cases:

Case	Actions
Case 1 - Create path	Calculate path from current position to the desired cabinet along predefined nodes (points) The calculated path consists of a list of nodes that have to be visited in the defined order
Case 2 - Proceed path	Get next node from path and set it as desired position
Case 3 - Drive to node	Drive robot to desired location by actuating the drivetrain of the robot
Case 4 - Break link	Break link between last and next node. Since the drivecontroller was unable to reach the desired node from the last node it is assumed to be blocked. This can be caused by a closed door or a static/dynamic object between the two nodes. In both cases when the path planner calculates a new path it is not desired to plan a path between those two nodes, therefore the link is removed
Case 5 - Reset links	No path is found, while it should be possible. This can be caused by the fact that some links between nodes are removed because it was not possible to drive from one to another. In case it was blocked by a dynamic object a path is possible after resetting all links if no links are reset, exit the program because recalculating a path doesn't make sense at this point

Cabinet_action phase

Figure 6: Cabinet_action phase

During the cabinet action phase the robot can interact with the cabinet.

The required interaction is specified in the competition and is consisting of taking a snapshot of the current laserdata and play a sound.

The flowchart of this phase is shown in figure 6.

Error phase

The error phase is only visited if something unrecoverably went wrong in the program, e.g. a required file is missing. In this phase the output of the drive motors is set to zero and the error is displayed to the user. Then the program is terminated

Software blocks

Task manager

The task manager functions as a finite state machine which switches between different tasks/states. It focuses mainly on the behavior of the whole program rather than the execution. It determines the next operation phase and case based on the current phase, current case, current block statuses and counters in which the corresponding block modes of the perceptor, path planner and drive controller are set for the upcoming execution. It communicates with the other blocks via the World model.

Since the "Escape room challenge" and the "Hospital competition" require a complete different approach in terms of cooperation between the blocks, the task planner is completely rewritten for both challenges.

ESCAPE ROOM CHALLENGE

BASIC BLOCK DIAGRAM :

INITIALIZATION:

The path planner is given a command “Drive_to_door” while the drive controller and the preceptor are given a command “Execute” as a part of the initialization process.

EXECUTION:

The high-level tasks “Drive_to_door”, “Drive_to_exit”, “Execute”, “Idle” and “Disable” were given to appropriate blocks as shown below:

KEY:

HOSPITAL ROOM CHALLENGE

FLOW CHART :

The function description can be found here : File:TASK MANAGERfin.pdf

Perceptor

The perceptor receives all of the incoming data from the pico robot and converts the data to useful data for the worldmodel. The incoming data exists of odometry data obtained by the wheel encoders of the pico robot. The laserdata obtained by the laser scanners. A Json file containing the global map and location of the cabinets, this file is provided a week before the hospital challenge. Moreover, the output of the perceptor to the world model consists of the global map, a local map, a combined map, the current/zero position and a close proximity region. The incoming data is handled within the perceptor by the following functions. A detailed description on what each function does in the preceptor and more information about the data flow can be found here.

The inputs and outputs of the perceptor are shown in the following figure:

The data used in the perceptor:

Path planner

The path planner determines the path for the PICO robot based on the combined map, the current location and the desired location. The planned path is a set of positions that the PICO robot is going to drive towards, this set is called the ‘next set of positions’. This next set of positions is saved in the world model and used by the task manager to send destination points to the drive controller.

If the path planner is idle, it is waiting for the task manager to start planning. Once the path planner is planning the path from the position of the PICO robot towards a given destination, the following things happen. First the map is gridded, creating all possible locations that the PICO robot is able to move towards. Then different paths are planned, for example through different doors. After that the most optimal path is planned and sent to the world model as next set of positions. When the PICO robot is following the path, the path planner checks if no unexpected objects are interfering with the planned trajectory.

The inputs, functions and outputs of the path planner are as follows:

A detailed description can be found here.

Drive controller

The drive Controller ensures that the pico robot drives to the desired location. It calculate the distance and direction to the desired location, relative to the current location. It checks if this direction is free of obstacles, if not it calculates an alternative direction that brings the pico robot closer to the desired destination. Finally it uses three PI controllers, one for each axis (rotational, X and Y) to calculate the desired speed for each axis and this is send to the pico-robot with the build-in function.

Inputs and outputs

Flow chart

The full details of the Drive Controller, including function descriptions can be found in the Drive Controller functionality description document found here.

Challenges

Escape Room Challenge

Our strategy for the escape room challenge was to use the software structure for the hospital challenge as much as possible. Therefore, the room is scanned from its initial position. From this location a local map of the room is created by the perceptor. Including, convex or concave corner points, doors and possible doors (if it is not fully certain the door is real). Based on this local map the task manager gives commands to the drive controller and path planner to position in front of the door. Once in front of the the possible door and verified as a real door the path planner sends the next position to the world model. Which is the end of the finish line in this case, which is detected by two lose ends of the walls. Also the robot is able to detect if there are objects in front of the robot to eventually avoid them.

Figure 7:Simulation of the escape room

Simulation and testing

Multiple possible maps where created and tested. In most of the cases the robot was able to escape the room. However, in some cases such as the room in the escape room challenge the robot could not escape. The cases were analyzed but there was enough time to implement these cases. Furthermore, the software was only partly tested with the real environment at the time of the escape room challenge. Each separate function worked, such as driving to destinations, making a local map with walls, doors and corner points, driving trough a hallway and avoiding obstacles.

What went good during the escape room challenge:

The robot was made robust, it could detect the walls even though a few walls were placed under a small angle and not straight next to each other. Furthermore, the graphical feedback in from of a local map was implemented on the “face” of the Pico. The Pico even drove to a possible door when later realizing this was not a door.

Improvements for the escape room challenge:

Doors can only be detected if it consists of convex corners, or two loose ends facing each other. In the challenge it was therefore not able to detect a possible door. The loose ends were not facing each other as can be seen in the gif below. Furthermore, there was not back up strategy when no doors where found, other then scanning the map again. Pico should have re-positioned itself somewhere else in the room or the pico could have followed a wall. However, we are not intending to use a wall follower in the hospital challenge. Therefore, this does not correspond with our chosen strategy. Another point that can be improved is creating the walls. For now walls can only be detected with a minimal number of laser points. Therefore, in the challenge it was not able to detect the small wall next to the corridor straight away. This was done to create a robust map but therefore also excluded some essential parts of the map.

In the simulation environment the map is recreated including the roughly placed walls. As expected in this simulation of the escape room the pico did not succeed to find the exit, the reasons are explained above.

Hospital Challenge

During the hospital challenge a list of cabinets is visited. The given order was 0, 1 and finally 3. Before this challenge a global map with coordinates of the cabinets was given. However there are doors that might be closed and unknown objects in the hospital. These objects can be either static or dynamic.

The software for the hospital challenge is an improved version of the software used during the escape room challenge. The same structure with blocks is used and as much as possible software is reused and adjusted where necessary. Major changes are done to the path planner and task manager since the hospital challenge is much more complex for those two blocks compared to the escape room challenge.

Video

TODO embed video. A higher quality version of the video can be found here: Hospital challenge - video group 2 - 2019

What went well

The things that went well where being able to detect the closed door and static object and being able to plan a path around the closed door and static obstacles. This is done by breaking the links between nodes, such that the path planning algorithm does not use these broken links anymore while planning a path. The broken links during the hospital challenge are visible in Figure 8, where all red lines between nodes indicate a broken link. Also did the localization work well, once it had determined the starting position correctly. This made it possible to determine the exact position of the PICO robot in the hospital during the challenge. Also was the localization robust against disturbances that were blocking it from detecting corners of rooms. This is also visible in Figure 8, where an object was blocking the top left corner of the room.

Figure 8: Broken links between nodes during hospital challenge

Improvements for the hospital challenge

The things that we would improve are improving the initial localization robustness since during the first try the localization was off, resulting in PICO getting stuck in the hallway. Luckily it did work correctly after a restart and we were able to finish. Also did we slightly hit the obstacle in the hallway, which was unexpected since a protection mechanism to avoid running into objects is implemented. Why this happened has to be investigated. The last improvement is increasing the speed during driving. The driving speed was lowered during the challenge to improve the robustness of the localization. If the localization is improved, the driving speed can be increased as well to finish the hospital challenge faster. The time duration can also be decreased by removing the delay while waiting at a cabinet, since this delay was set to 5 seconds.

Code snippets

• Main
• Fit lines on laserdata