Skills

A skill is a subtask of a robot program application. In its simplest version a skill consists only of one of pitasc’s basic skill types, e.g. a skill_lin: move linearly from point A to point B. But a skill can also be composed out of multiple skills to create a more complex compound skill. Skills are also able to inherit from other skills.

Defined at file models/coordination.xml in package pitasc_library.

General structure

Chain of prototype based inheritance

any_skills --> (skill_single_robot) --> skill --> object --> dictionary --> base --> descriptive

All skills are inheriting from ‘skill’, but most skills are inheriting from ‘skill_single_robot’.

Skills contain the following attributes inside the <type> tag.

Attributes inside `<type>` tag
Attribute	Description
id	Needs to be locally unique to allow identification. If not unique, a incrementing element e.g., “_no0”, “_no1”, “_no2”, … will be added
data_type	Already set by inheritance (dict)
prototype	The base type the skill “inherits” from, e.g. “skill_cartesian”.

Skills contain the following parameters inside the <meta> tag.

Members inside `<meta>` tag
Member	Description
description	Describes the function of the skill.
implementation	Implementation details already set by inheritance.
categories	Categories the skill is part of (e.g. single_robot, dual_robot, position_controlled, force_controlled, velocity_controlled).
visibility	Visibility of the skill (enum: required, basic, expert, hidden).

Skills contain the following parameters inside the <data> tag.

Members inside `<data>` tag
Member	Description
skill_name	Name of this skill. It must be locally unique.
monitors	Contains the monitors of the skill that determine when the skill should terminate.
transitions	Contains additional transitions to other states (skills), given an event name.
scripts	Contains scripts that should be executed while the skill is active.
collections	Contains the kinematic chains of the skill (feature, robot, object chains).
loops	Contains the kinematic loop(s) that define the task to be solved.
tasks	Contains the task description(s).
bounds	Contains the bounds description(s).

For more information on the expert parameters, see A Prototype-Based Skill Model for Specifying Robotic Assembly Tasks.

The xml definition of a skill basically looks like the following:

<type id= '{Choose unique id}' prototype= '{Add parent skill id}'> <!-- reference here -->
    <meta>
        <member id="description"> {Choose meaningful description} </member>
        <member id="categories"> {Add category(s) separated by comma} </member>
        <member id="visibility"> {Choose enum} </member>
    </meta>
    <data>
        <member id="skill_name"> {Choose name} </member>
        <member id="collections"> {Add collection element(s)} </member>
        <member id="loops"> {Add loop element(s)} </member>
        <member id="tasks"> {Add task element(s)} </member>
        <member id="bounds"> {Add bound element(s)} </member>
        <member id="monitors"> {Add monitor element(s)} </member>
        <member id="transitions"> {Add transition element(s)} </member>
        <member id="scripts"> {Add script element(s)} </member>
    </data>
</type>

For example, a skill which moves the tool frame along three waypoints to form a triangle could look like this:

<pitasc>
    <models>
        <include package="pitasc_library" file="models/pitasc.xml"/>
        <include package="pitasc_library" file="skills/skill_lin.xml"/>

        <type id="skill_move_triangle" prototype="skill_sequence">
            <meta>
                <member id="description">Moves along the given three frames to form a triangle</member>
                <member id="categories">single_robot, position_controlled</member>
                <member id="visibility">basic</member>
            </meta>

            <data>

                <type id="tool_frame" prototype="frame">
                    <meta>
                        <member id="description">Name of the tool frame</member>
                        <member id="visibility">required</member>
                    </meta>
                </type>

                <type id="frame_1" prototype="frame">
                    <meta>
                        <member id="description">Name of the first frame</member>
                        <member id="visibility">required</member>
                    </meta>
                </type>

                <type id="frame_2" prototype="frame">
                    <meta>
                        <member id="description">Name of the second frame</member>
                        <member id="visibility">required</member>
                    </meta>
                </type>

                <type id="frame_1" prototype="frame">
                    <meta>
                        <member id="description">Name of the third frame</member>
                        <member id="visibility">required</member>
                    </meta>
                </type>

                <member id="skills">
                    <clone prototype="skill_lin">
                        <member id="tool_frame" reference_id="tool_frame" />
                        <member id="target_frame" reference_id="frame_1" />
                    </clone>
                    <clone prototype="skill_lin">
                        <member id="tool_frame" reference_id="tool_frame" />
                        <member id="target_frame" reference_id="frame_2" />
                    </clone>
                    <clone prototype="skill_lin">
                        <member id="tool_frame" reference_id="tool_frame" />
                        <member id="target_frame" reference_id="frame_3" />
                    </clone>
                    <clone prototype="skill_lin">
                        <member id="tool_frame" reference_id="tool_frame" />
                        <member id="target_frame" reference_id="frame_1" />
                    </clone>
                </member>

            </data>
        </type>
    </models>
</pitasc>

Note