BasicGPM Class Reference

Implements a Gradient Projection Method (GPM) More...

#include <BasicGPM.hpp>

Public Types
enum	ProjectionFrame { BaseFrame = 0 , ControlFrame }
	Enumeration used to specify frame associated with the projection. More...

Public Member Functions
	BasicGPM (rw::models::Device *device, rw::core::Ptr< rw::kinematics::Frame > controlFrame, const rw::kinematics::State &state, const rw::math::Q &qhome, double dt)
	Constructs BasicGPM object. More...
virtual	~BasicGPM ()
	Destructor.
rw::math::Q	solve (const rw::math::Q &q, const rw::math::Q &dq, const rw::math::VelocityScrew6D<> &tcpvel)
	Solves for joint velocities given a desired tool velocity. More...
void	setUseJointLimitsCost (bool use)
	Specifies whether to use joint limit avoidance. More...
void	setUseSingularityCost (bool use)
	Specifies whether to use singularity avoidance. More...
void	setJointLimitsWeight (double w)
	Sets the weight of the joint limits. More...
void	setJointLimitThreshold (double thresholdLowerRatio, double thresholdUpperRatio)
	Sets the threshold for the joint limits. More...
void	setSingularityWeight (double w)
	Sets the weight of the singularity avoidance task. More...
void	setProjection (const Eigen::MatrixXd &P, ProjectionFrame space)
	Setup the projection. More...

Detailed Description

Implements a Gradient Projection Method (GPM)

GPM implements the basic Gradient Projection Method with joint limit and singularity avoidance presented in [1]: "Using the task function approach to avoid robot joint limits and kinematic singularities in visual servoing" by Marchand, Chaumette and Rizzo, IEEE/RSJ Int. Conf. on Intelligent Robots and Systems, 1996, vol. 3, pp. 1083-1090.

Member Enumeration Documentation

ProjectionFrame

enum ProjectionFrame

Enumeration used to specify frame associated with the projection.

Enumerator
ControlFrame	Robot Base Frame The Frame specified as the controlFrame

Constructor & Destructor Documentation

BasicGPM()

BasicGPM	(	rw::models::Device *	device,
		rw::core::Ptr< rw::kinematics::Frame >	controlFrame,
		const rw::kinematics::State &	state,
		const rw::math::Q &	qhome,
		double	dt
	)

Constructs BasicGPM object.

Parameters

device	[in] Device to work with
controlFrame	[in] The frame on the device to control. Usually this will be the tool, but not necessarily.
state	[in] Default state
qhome	[in] Configuration somewhere between the lower and upper limit and towards which the joints should move
dt	[in] Step size

Member Function Documentation

setJointLimitsWeight()

void setJointLimitsWeight

(

double

w

)

Sets the weight of the joint limits.

Parameters

w	[in] Weight of the joint limit

setJointLimitThreshold()

void setJointLimitThreshold	(	double	thresholdLowerRatio,
		double	thresholdUpperRatio
	)

Sets the threshold for the joint limits.

Given an upper and a lower bound \(upper\) and \(lower\) the proximity of the joint limits is defined as \(upper-\tau_{max} (upper-lower)\) and \(lower+\tau_{min} (upper-lower)\) where \(\tau_{min}\) and \(\tau_{max}\) are the thresholds specified here.

Parameters

thresholdLowerRatio	[in] Relative threshold for the lower joint limits
thresholdUpperRatio	[in] Relative threshold for the upper joint limits

setProjection()

void setProjection	(	const Eigen::MatrixXd &	P,
		ProjectionFrame	space
	)

Setup the projection.

The traditional relationship between device Jacobian, joint velocities and tool velocity is given by \(J\dot{q}=\dot{q}\). To ignore certain degrees of freedom or put more emphasis (with respect to the least square solution) on some we can multiply with \(P\) to get \(P J\dot{q}=P \dot{x}\).

\(P\) needs to have exactly 6 columns, however the number of row may be less than 6. Use the space flag to specify in which space the projection should occur.

Usage: Setup to ignore tool roll

BasicGPM* gpm = new BasicGPM(device, device->getEnd(), state, qhome, dt)
Eigen::MatrixXd P = Eigen::MatrixXd::Zero(5,6);
for (int i = 0; i<5; i++)
    P(i,i) = 1;
gpm->setProjection(P, BasicGPM::ControlFrame);

Parameters

P	[in] The projection matrix
space	[in] The space in which to apply the projection

setSingularityWeight()

void setSingularityWeight

(

double

w

)

Sets the weight of the singularity avoidance task.

Parameters

w	[in] The weight

setUseJointLimitsCost()

void setUseJointLimitsCost

(

bool

use

)

Specifies whether to use joint limit avoidance.

The method implements the method with Activation threshold from the [1]

Parameters

use	[in] True to use joint limit avoidance

setUseSingularityCost()

void setUseSingularityCost

(

bool

use

)

Specifies whether to use singularity avoidance.

The singularity avoidance as described in [1]

Parameters

use	[in] True to use singularity avoidance

solve()

rw::math::Q solve	(	const rw::math::Q &	q,
		const rw::math::Q &	dq,
		const rw::math::VelocityScrew6D<> &	tcpvel
	)

Solves for joint velocities given a desired tool velocity.

Parameters

q	[in] The current joint configuration
dq	[in] The current joint velocity
tcpvel	[in] The desired tool velocity seen in the base frame

---

The documentation for this class was generated from the following file:

• BasicGPM.hpp