Implementation of a differential transmission. More...

#include <differential_transmission.hpp>

Inheritance diagram for transmission_interface::DifferentialTransmission:

Collaboration diagram for transmission_interface::DifferentialTransmission:

Public Member Functions
	DifferentialTransmission (const std::vector< double > &actuator_reduction, const std::vector< double > &joint_reduction, const std::vector< double > &joint_offset={0.0, 0.0})

void	configure (const std::vector< JointHandle > &joint_handles, const std::vector< ActuatorHandle > &actuator_handles) override

void	actuator_to_joint () override
	Transform variables from actuator to joint space.

void	joint_to_actuator () override
	Transform variables from joint to actuator space.

std::size_t	num_actuators () const override

std::size_t	num_joints () const override

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

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

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

std::string	get_handles_info () const
	Get human-friendly report of handles.

Protected Attributes
std::vector< double >	actuator_reduction_

std::vector< double >	joint_reduction_

std::vector< double >	joint_offset_

std::vector< JointHandle >	joint_position_

std::vector< JointHandle >	joint_velocity_

std::vector< JointHandle >	joint_effort_

std::vector< ActuatorHandle >	actuator_position_

std::vector< ActuatorHandle >	actuator_velocity_

std::vector< ActuatorHandle >	actuator_effort_

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:

\( x \), \( \dot{x} \) and \( \tau \) are position, velocity and effort variables, respectively.
Subindices \( _a \) and \( _j \) 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).
\( n \) 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 \( (0, 1) \) 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.

Constructor & Destructor Documentation

◆ DifferentialTransmission()

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

inline

Parameters

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

Precondition: Nonzero actuator and joint reduction values.

Member Function Documentation

◆ actuator_to_joint()

void transmission_interface::DifferentialTransmission::actuator_to_joint ( )

inlineoverridevirtual

Transform variables from actuator to joint space.

Precondition: Actuator and joint 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.

◆ configure()

void transmission_interface::DifferentialTransmission::configure	(	const std::vector< JointHandle > &	joint_handles,
		const std::vector< ActuatorHandle > &	actuator_handles
	)

overridevirtual

Parameters

[in]	joint_handles	Handles of joint values.
[in]	actuator_handles	Handles of actuator values.

Precondition: Handles are valid and matching in size

Implements transmission_interface::Transmission.

◆ joint_to_actuator()

void transmission_interface::DifferentialTransmission::joint_to_actuator ( )

inlineoverridevirtual

Transform variables from joint to actuator space.

Precondition: Actuator and joint 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.

◆ num_actuators()

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

inlineoverridevirtual

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

Implements transmission_interface::Transmission.

◆ num_joints()

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

inlineoverridevirtual

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

Implements transmission_interface::Transmission.

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

ros2_control/transmission_interface/include/transmission_interface/differential_transmission.hpp

	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

◆ DifferentialTransmission()

Member Function Documentation

◆ actuator_to_joint()

◆ configure()

◆ joint_to_actuator()

◆ num_actuators()

◆ num_joints()