Implementation of a differential transmission. More...

#include <differential_transmission.h>

Inheritance diagram for transmission_interface::DifferentialTransmission:

Public Member Functions
void	actuatorToJointEffort (const ActuatorData &act_data, JointData &jnt_data)
	Transform effort variables from actuator to joint space. More...

void	actuatorToJointPosition (const ActuatorData &act_data, JointData &jnt_data)
	Transform position variables from actuator to joint space. More...

void	actuatorToJointVelocity (const ActuatorData &act_data, JointData &jnt_data)
	Transform velocity variables from actuator to joint space. More...

	DifferentialTransmission (const std::vector< double > &actuator_reduction, const std::vector< double > &joint_reduction, const std::vector< double > &joint_offset=std::vector< double >(2, 0.0))

const std::vector< double > &	getActuatorReduction () const

const std::vector< double > &	getJointOffset () const

const std::vector< double > &	getJointReduction () const

void	jointToActuatorEffort (const JointData &jnt_data, ActuatorData &act_data)
	Transform effort variables from joint to actuator space. More...

void	jointToActuatorPosition (const JointData &jnt_data, ActuatorData &act_data)
	Transform position variables from joint to actuator space. More...

void	jointToActuatorVelocity (const JointData &jnt_data, ActuatorData &act_data)
	Transform velocity variables from joint to actuator space. More...

std::size_t	numActuators () const

std::size_t	numJoints () const

Public Member Functions inherited from transmission_interface::Transmission
virtual	~Transmission ()

Protected Attributes
std::vector< double >	act_reduction_

std::vector< double >	jnt_offset_

std::vector< double >	jnt_reduction_

Detailed Description

Implementation of a differential transmission.

This transmission relates two actuators and two joints through a differential mechanism, as illustrated below.

	Effort	Velocity	Position
Actuator to joint	$\begin{eqnarray} \tau_{j_1} & = & n_{j_1} ( n_{a_1} \tau_{a_1} + n_{a_2} \tau_{a_2} ) \\[2.5em] \tau_{j_2} & = & n_{j_2} ( n_{a_1} \tau_{a_1} + n_{a_2} \tau_{a_2} ) \end{eqnarray}$	$\begin{eqnarray} \dot{x}_{j_1} & = & \frac{ \dot{x}_{a_1} / n_{a_1} + \dot{x}_{a_2} / n_{a_2} }{2 n_{j_1}} \\[1em] \dot{x}_{j_2} & = & \frac{ \dot{x}_{a_1} / n_{a_1} - \dot{x}_{a_2} / n_{a_2} }{2 n_{j_2}} \end{eqnarray}$	$\begin{eqnarray} x_{j_1} & = & \frac{ x_{a_1} / n_{a_1} + x_{a_2} / n_{a_2} }{2 n_{j_1}} + x_{off_1} \\[1em] x_{j_2} & = & \frac{ x_{a_1} / n_{a_1} - x_{a_2} / n_{a_2} }{2 n_{j_1}} + x_{off_2} \end{eqnarray}$
Joint to actuator	$\begin{eqnarray} \tau_{a_1} & = & \frac{ \tau_{j_1} / n_{j_1} + \tau_{j_2} / n_{j_2} }{2 n_{a_1}} \\[1em] \tau_{a_2} & = & \frac{ \tau_{j_1} / n_{j_1} - \tau_{j_2} / n_{j_2} }{2 n_{a_1}} \end{eqnarray}$	$\begin{eqnarray} \dot{x}_{a_1} & = & n_{a_1} ( n_{j_1} \dot{x}_{j_1} + n_{j_2} \dot{x}_{j_2} ) \\[2.5em] \dot{x}_{a_2} & = & n_{a_2} ( n_{j_1} \dot{x}_{j_1} - n_{j_2} \dot{x}_{j_2} ) \end{eqnarray}$	$\begin{eqnarray} x_{a_1} & = & n_{a_1} \left[ n_{j_1} (x_{j_1} - x_{off_1}) + n_{j_2} (x_{j_2} - x_{off_2}) \right] \\[2.5em] x_{a_2} & = & n_{a_2} \left[ n_{j_1} (x_{j_1} - x_{off_1}) - n_{j_2} (x_{j_2} - x_{off_2}) \right] \end{eqnarray}$

where:

, $\dot{x}$ and $\tau$ are position, velocity and effort variables, respectively.
Subindices and are used to represent actuator-space and joint-space variables, respectively.
$x_{off}$ represents the offset between motor and joint zeros, expressed in joint position coordinates (cf. SimpleTransmission class documentation for a more detailed description of this variable).
represents a transmission ratio. Reducers/amplifiers are allowed on both the actuator and joint sides (depicted as timing belts in the figure). A transmission ratio can take any real value except zero. In particular:
- If its absolute value is greater than one, it's a velocity reducer / effort amplifier, while if its absolute value lies in it's a velocity amplifier / effort reducer.
- Negative values represent a direction flip, ie. input and output move in opposite directions.
- Important: Use transmission ratio signs to match this class' convention of positive actuator/joint directions with a given mechanical design, as they will in general not match.

Note: This implementation currently assumes a specific layout for location of the actuators and joint axes which is common in robotic mechanisms. Please file an enhancement ticket if your use case does not adhere to this layout.

Definition at line 117 of file differential_transmission.h.

Constructor & Destructor Documentation

transmission_interface::DifferentialTransmission::DifferentialTransmission	(	const std::vector< double > &	actuator_reduction,
		const std::vector< double > &	joint_reduction,
		const std::vector< double > &	joint_offset = `std::vector<double>(2, 0.0)`
	)

inline

Parameters

actuator_reduction	Reduction ratio of actuators.
joint_reduction	Reduction ratio of joints.
joint_offset	Joint position offset used in the position mappings.

Precondition: Nonzero actuator and joint reduction values.

Definition at line 203 of file differential_transmission.h.

Member Function Documentation

void transmission_interface::DifferentialTransmission::actuatorToJointEffort	(	const ActuatorData &	act_data,
		JointData &	jnt_data
	)

inlinevirtual

Transform effort variables from actuator to joint space.

Parameters

[in]	act_data	Actuator-space variables.
[out]	jnt_data	Joint-space variables.

Precondition: Actuator and joint effort vectors must have size 2 and point to valid data. To call this method it is not required that all other data vectors contain valid data, and can even remain empty.

Implements transmission_interface::Transmission.

Definition at line 228 of file differential_transmission.h.

void transmission_interface::DifferentialTransmission::actuatorToJointPosition	(	const ActuatorData &	act_data,
		JointData &	jnt_data
	)

inlinevirtual

Transform position variables from actuator to joint space.

Parameters

[in]	act_data	Actuator-space variables.
[out]	jnt_data	Joint-space variables.

Precondition: Actuator and joint position vectors must have size 2 and point to valid data. To call this method it is not required that all other data vectors contain valid data, and can even remain empty.

Implements transmission_interface::Transmission.

Definition at line 254 of file differential_transmission.h.

void transmission_interface::DifferentialTransmission::actuatorToJointVelocity	(	const ActuatorData &	act_data,
		JointData &	jnt_data
	)

inlinevirtual

Transform velocity variables from actuator to joint space.

Parameters

[in]	act_data	Actuator-space variables.
[out]	jnt_data	Joint-space variables.

Precondition: Actuator and joint velocity vectors must have size 2 and point to valid data. To call this method it is not required that all other data vectors contain valid data, and can even remain empty.

Implements transmission_interface::Transmission.

Definition at line 241 of file differential_transmission.h.

const std::vector<double>& transmission_interface::DifferentialTransmission::getActuatorReduction ( ) const

inline

Definition at line 193 of file differential_transmission.h.

const std::vector<double>& transmission_interface::DifferentialTransmission::getJointOffset ( ) const

inline

Definition at line 195 of file differential_transmission.h.

const std::vector<double>& transmission_interface::DifferentialTransmission::getJointReduction ( ) const

inline

Definition at line 194 of file differential_transmission.h.

void transmission_interface::DifferentialTransmission::jointToActuatorEffort	(	const JointData &	jnt_data,
		ActuatorData &	act_data
	)

inlinevirtual

Transform effort variables from joint to actuator space.

Parameters

[in]	jnt_data	Joint-space variables.
[out]	act_data	Actuator-space variables.

Precondition: Actuator and joint effort vectors must have size 2 and point to valid data. To call this method it is not required that all other data vectors contain valid data, and can even remain empty.

Implements transmission_interface::Transmission.

Definition at line 267 of file differential_transmission.h.

void transmission_interface::DifferentialTransmission::jointToActuatorPosition	(	const JointData &	jnt_data,
		ActuatorData &	act_data
	)

inlinevirtual

Transform position variables from joint to actuator space.

Parameters

[in]	jnt_data	Joint-space variables.
[out]	act_data	Actuator-space variables.

Precondition: Actuator and joint position vectors must have size 2 and point to valid data. To call this method it is not required that all other data vectors contain valid data, and can even remain empty.

Implements transmission_interface::Transmission.

Definition at line 293 of file differential_transmission.h.

void transmission_interface::DifferentialTransmission::jointToActuatorVelocity	(	const JointData &	jnt_data,
		ActuatorData &	act_data
	)

inlinevirtual

Transform velocity variables from joint to actuator space.

Parameters

[in]	jnt_data	Joint-space variables.
[out]	act_data	Actuator-space variables.

Precondition: Actuator and joint velocity vectors must have size 2 and point to valid data. To call this method it is not required that all other data vectors contain valid data, and can even remain empty.

Implements transmission_interface::Transmission.

Definition at line 280 of file differential_transmission.h.

std::size_t transmission_interface::DifferentialTransmission::numActuators ( ) const

inlinevirtual

Returns: Number of actuators managed by transmission, ie. the dimension of the actuator space.

Implements transmission_interface::Transmission.

Definition at line 190 of file differential_transmission.h.

std::size_t transmission_interface::DifferentialTransmission::numJoints ( ) const

inlinevirtual

Returns: Number of joints managed by transmission, ie. the dimension of the joint space.

Implements transmission_interface::Transmission.

Definition at line 191 of file differential_transmission.h.

Member Data Documentation

std::vector<double> transmission_interface::DifferentialTransmission::act_reduction_

protected

Definition at line 198 of file differential_transmission.h.

std::vector<double> transmission_interface::DifferentialTransmission::jnt_offset_

protected

Definition at line 200 of file differential_transmission.h.

std::vector<double> transmission_interface::DifferentialTransmission::jnt_reduction_

protected

Definition at line 199 of file differential_transmission.h.

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

differential_transmission.h

	Effort	Velocity	Position
Actuator to joint	$\begin{eqnarray} \tau_{j_1} & = & n_{j_1} ( n_{a_1} \tau_{a_1} + n_{a_2} \tau_{a_2} ) \\[2.5em] \tau_{j_2} & = & n_{j_2} ( n_{a_1} \tau_{a_1} + n_{a_2} \tau_{a_2} ) \end{eqnarray}$	$\begin{eqnarray} \dot{x}_{j_1} & = & \frac{ \dot{x}_{a_1} / n_{a_1} + \dot{x}_{a_2} / n_{a_2} }{2 n_{j_1}} \\[1em] \dot{x}_{j_2} & = & \frac{ \dot{x}_{a_1} / n_{a_1} - \dot{x}_{a_2} / n_{a_2} }{2 n_{j_2}} \end{eqnarray}$	$\begin{eqnarray} x_{j_1} & = & \frac{ x_{a_1} / n_{a_1} + x_{a_2} / n_{a_2} }{2 n_{j_1}} + x_{off_1} \\[1em] x_{j_2} & = & \frac{ x_{a_1} / n_{a_1} - x_{a_2} / n_{a_2} }{2 n_{j_1}} + x_{off_2} \end{eqnarray}$
Joint to actuator	$\begin{eqnarray} \tau_{a_1} & = & \frac{ \tau_{j_1} / n_{j_1} + \tau_{j_2} / n_{j_2} }{2 n_{a_1}} \\[1em] \tau_{a_2} & = & \frac{ \tau_{j_1} / n_{j_1} - \tau_{j_2} / n_{j_2} }{2 n_{a_1}} \end{eqnarray}$	$\begin{eqnarray} \dot{x}_{a_1} & = & n_{a_1} ( n_{j_1} \dot{x}_{j_1} + n_{j_2} \dot{x}_{j_2} ) \\[2.5em] \dot{x}_{a_2} & = & n_{a_2} ( n_{j_1} \dot{x}_{j_1} - n_{j_2} \dot{x}_{j_2} ) \end{eqnarray}$	$\begin{eqnarray} x_{a_1} & = & n_{a_1} \left[ n_{j_1} (x_{j_1} - x_{off_1}) + n_{j_2} (x_{j_2} - x_{off_2}) \right] \\[2.5em] x_{a_2} & = & n_{a_2} \left[ n_{j_1} (x_{j_1} - x_{off_1}) - n_{j_2} (x_{j_2} - x_{off_2}) \right] \end{eqnarray}$

Public Member Functions

Protected Attributes

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation