Retake Embedded Motion Control 2018 Nr2

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TU/e Number Name E-mail
1036818 Rokesh Gajapathy

Introduction and Problem Definition

Figure 1: PICO

The motivation for "Follow Me!" project is to develop a software architecture for PICO to assist elderly person in carrying the objects and follow the person to the desired position. In this project, three levels are defined to achieve the goal in a robust manner. The elderly person is defined as a Person Of Interest (POI), static obstacles and actors are all part of the environment (World).

PICO must follow the POI, POI will not move at a speed more than 0.5 m/s (i.e) approximately 0.75 step/second. PICO should follow the POI at a distance of 0.4 m. The level one task was only designed, developed, implemented and tested. In level one, the PICO should follow the POI with the disturbances of actor in the environment. The actor cannot occlude the POI (i.e) should not come in between the POI and PICO.

Figure 2: A situation which can not occur for Level 1. In red we see PICO, blue the POI, and in darkgreen the actor.

The POI should pass through the middle of the target strips as shown in Figure 3, the number of target strips will be around 5. PICO should pass through 80 % of the target strip.

Figure 3: A sketch of the setup. The pre-defined path is indicated by the dashed lines, the target strips by the black lines perpendicular to the pre-defined path, the POI that follows the pre-defined path in blue, and PICO in red.

Initial Design

The initial design section gives an overview of the various design decisions taken to achieve the desired results. The requirements for completing the task with available resources is defined followed by the state machine and finally functional components required to achieve the state machine defined.

Available Resources

Specification Value Unit
Detectable Distance 0.01 to 10 meters [m]
Scanning Angle -2 to 2 radians [rad]
Angular Resolution 0.004004 radians [rad]
Distance between POI and PICO 0.4 meters [m]
Speed of POI 0.5 meter/second [m/s]
Width of target strip 1 meter [m]

Design Decisions

From the available resources and problem definition important design decisions are taken as follows:

1. The maximum detectable distance and scanning angle is constrained to 1 m and 90 degree respectively because the length of the target strip is 1 m, a equilateral triangle is drawn with respect to LRF center which is 60 degree for center, 15 degrees for left and degree right respectively.

2. The reference frame [math]\displaystyle{ (x_r,y_r) }[/math] and base frame [math]\displaystyle{ (x_b,y_b) }[/math] is defined as POI and PICO respectively. Since PICO need to follow the POI (i.e) go forward or rotate with respect to the POI.

3. The PICO moves at a speed of 0.5 m/s and rotates at 2 rad/s because the POI walks at speed of 0.5 m/s.

4. Stopping distance is 0.4 m (i.e) if the distance between POI and PICO less than 0.4 m PICO stops obtained from the problem statement

5. The delectable sensor range is split into three components left,center and right to tackle the disturbances (i.e) Actors.

Figure 4: PICO Design Decisions


Function Action Validation
Identify the POI (reference frame) Two legs are identified which is close to PICO (base frame) Visualize using lase range points, see
Follow the POI Follow the POI at a distance of 0.4 m at a speed of 0.5 m/s Walk straight in-front of the PICO
Rotate with respect to POI Base frame (PICO) rotates with respect to the reference frame (POI) at 2 rad/s Walk right and left side in-front of the PICO
Stop when POI stops PICO stops when the distance between POI and PICO less than 0.4 m Stop while walking in-front of PICO
Stop when POI stops PICO stops when the distance between POI and PICO less than 0.4 m Stop while walking in-front of PICO
Do not follow the Actors Scanning Angle is constrained to 60 degree and if legs are identified in the right or left side of the PICO, it follows the one in center. Actors walk on the side of the robot not in between the PICO and POI

Finite State Machine

Figure 5: State Flow Diagram

Software Architecture

The software that will be deployed on PICO can be categorized in four different components: perception, monitoring, plan and control. They exchange information through the world model, which stores all the data. The software will have just one thread and it will execute the four components in a loop: first perception, then monitoring, plan, and control. The loop is executed at a rate of 20 Hz (i.e) for every 50 milliseconds.


Results and Conclusion