Stanford Whole-Body Control Framework: opspace::Task Class Reference

List of all members.


Public Member Functions
virtual Status	init (Model const &model)=0
	Abstract, implemented by subclasses in order to initialize the task.
virtual Status	update (Model const &model)=0
	Abstract, implemented by subclasses in order to compute the current task state, the command acceleration, and the Jacobian.
Vector const &	getActual () const
	Returns: The actual "position" of the robot in this task space.
Vector const &	getCommand () const
	Returns: The command of this task.
Matrix const &	getJacobian () const
	Returns: The current Jacobian of this task space.
double	getSigmaThreshold () const
	SVD cutoff value for pseudo inverse, exists in all tasks because Controller implementations need it.
virtual void	dump (std::ostream &os, std::string const &title, std::string const &prefix) const
virtual void	dbg (std::ostream &os, std::string const &title, std::string const &prefix) const
Protected Member Functions
	Task (std::string const &name)
Protected Attributes
Vector	actual_
Vector	command_
Matrix	jacobian_
double	sigma_threshold_
	Parameter "sigma_threshold", SVD cutoff value for pseudo inverse.

Detailed Description

The base class provides parameter introspection facilities and an interface that is used by opspace::Controller instances to come up with control signals for a robot.

This is one of the most important classes in the opspace namespace. You implement tasks by subclassing from it (or one of its more specialized derivatives) and implementing the init() and update() methods. You can also override some other methods if you are not happy with the defaults.

  class Thermostat : public Task {
  public:
    Thermostat(std::string const & name) : Task(name), temp_(0) {
      declareParameter("desired_temperature", &temp_);
    }
    
    virtual Status init(Model const & model) {
      if (1 != model.getNDOF()) {
  return Status(false, "are you sure this is a fridge?");
      }
      jacobian_ = Vector::Ones(1); // somewhat spurious in this example
      command_ = Vector::Zero(1);
      return update(model);
    }
    
    virtual Status update(Model const & model) {
      actual_ = model.getState().position_;
      if (actual_[0] > temp_) {
  command_[0] = 1;
      }
      else {
  command_[0] = 0;
      }
      // jacobian_ was set in init() and never changes in this example
      Status ok;
      return ok;
    }
    
  private:
    double temp_;
  };

Constructor & Destructor Documentation

opspace::Task::Task ( std::string const & name ) [explicit, protected]

Definition at line 34 of file Task.cpp.

References actual_, command_, opspace::ParameterReflection::declareParameter(), and sigma_threshold_.

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Member Function Documentation

virtual Status opspace::Task::init ( Model const & model ) [pure virtual]

Abstract, implemented by subclasses in order to initialize the task.

This is important for stateful tasks, for instance in order to initialize a trajectory-following behavior. The init() method also gets called when tasks are switched at runtime, so subclasses should NOT assume that init() only gets called once at startup.

Implemented in opspace::DraftPIDTask, opspace::CartPosTask, opspace::JPosTask, opspace::SelectedJointPostureTask, opspace::CartPosTrjTask, opspace::JPosTrjTask, opspace::JointLimitTask, opspace::OrientationTask, tut02::JTask, tut03::JTask, tut04::JTask, and tut05::PTask.

virtual Status opspace::Task::update ( Model const & model ) [pure virtual]

Abstract, implemented by subclasses in order to compute the current task state, the command acceleration, and the Jacobian.

Given the current joint-space model passed as argument to this method, subclasses have to set the actual_, command_, and jacobian_ fields. These will then get retrieved according to the task hierarchy and assembled into joint torque commands using dynamically consistent nullspace projection.

Note:: Make sure your subclass sets the actual_, command_, and jacobian_ fields in the implementation of this method.

Vector const& opspace::Task::getActual ( ) const [inline]

Returns:: The actual "position" of the robot in this task space.

Reminder: actual_ must be set by subclasses in their update() method.

Definition at line 124 of file Task.hpp.

References actual_.

Vector const& opspace::Task::getCommand ( ) const [inline]

Returns:: The command of this task.

In the operational space formulation, this is simply the desired acceleration of the task point (in task space, of course). Reminder: command_ must be set by subclasses in their update() method.

Definition at line 132 of file Task.hpp.

References command_.

Referenced by opspace::ClassicTaskPostureController::computeCommand(), and servo_cb().

Matrix const& opspace::Task::getJacobian ( ) const [inline]

Returns:: The current Jacobian of this task space.

The Jacobian maps joint velocities to task space velocities (it thus has M rows and N columns, where M is the dimension of the task space and N the number of degrees of freedom of the robot). Usually, the Jacobian is configuration dependent and is updated along with the command in the update() method. Some tasks, however, have simple and constant Jacobians which can be set in the init() method. The Jacobian is used by the opspace::Controller to compensate for rigid body dynamics and to decouple tasks according to a strict hierarchy. Reminder: jacobian_ must be set by subclasses in their update() method.

Definition at line 147 of file Task.hpp.

References jacobian_.

Referenced by opspace::ClassicTaskPostureController::computeCommand(), and servo_cb().

double opspace::Task::getSigmaThreshold ( ) const [inline]

SVD cutoff value for pseudo inverse, exists in all tasks because Controller implementations need it.

Definition at line 153 of file Task.hpp.

References sigma_threshold_.

Referenced by opspace::TaskPostureTrjSkill::checkJStarSV(), opspace::TaskPostureSkill::checkJStarSV(), and opspace::ClassicTaskPostureController::computeCommand().