Implementation of a differential transmission. More...

#include <differential_transmission.h>

Inheritance diagram for transmission_interface::DifferentialTransmission:

Public Member Functions
void	actuatorToJointAbsolutePosition (const ActuatorData &act_data, JointData &jnt_data) override
	Transform absolute encoder values from actuator to joint space. More...

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

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

void	actuatorToJointTorqueSensor (const ActuatorData &act_data, JointData &jnt_data) override
	Transform torque sensor values from actuator to joint space. More...

void	actuatorToJointVelocity (const ActuatorData &act_data, JointData &jnt_data) override
	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)

	DifferentialTransmission (const std::vector< double > &actuator_reduction, const std::vector< double > &joint_reduction, bool ignore_transmission_for_absolute_encoders=false, 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

bool	hasActuatorToJointAbsolutePosition () const override

bool	hasActuatorToJointTorqueSensor () const override

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

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

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

std::size_t	numActuators () const override

std::size_t	numJoints () const override

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

Protected Attributes
std::vector< double >	act_reduction_

bool	ignore_transmission_for_absolute_encoders_

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

◆ DifferentialTransmission() [1/2]

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

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 238 of file differential_transmission.h.

◆ DifferentialTransmission() [2/2]

transmission_interface::DifferentialTransmission::DifferentialTransmission	(	const std::vector< double > &	actuator_reduction,
		const std::vector< double > &	joint_reduction,
		bool	ignore_transmission_for_absolute_encoders = `false`,
		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.
ignore_transmission_for_absolute_encoders	Whether to take the data directly from absolute encoders instead of calculating through transmission.
joint_offset	Joint position offset used in the position mappings.

Precondition: Nonzero actuator and joint reduction values.

Definition at line 244 of file differential_transmission.h.

Member Function Documentation

◆ actuatorToJointAbsolutePosition()

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

inlineoverridevirtual

Transform absolute encoder values from actuator to joint space.

Parameters

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

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

Reimplemented from transmission_interface::Transmission.

Definition at line 308 of file differential_transmission.h.

◆ actuatorToJointEffort()

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

inlineoverridevirtual

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 269 of file differential_transmission.h.

◆ actuatorToJointPosition()

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

inlineoverridevirtual

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 295 of file differential_transmission.h.

◆ actuatorToJointTorqueSensor()

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

inlineoverridevirtual

Transform torque sensor values from actuator to joint space.

Parameters

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

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

Reimplemented from transmission_interface::Transmission.

Definition at line 329 of file differential_transmission.h.

◆ actuatorToJointVelocity()

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

inlineoverridevirtual

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 282 of file differential_transmission.h.

◆ getActuatorReduction()

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

inline

Definition at line 227 of file differential_transmission.h.

◆ getJointOffset()

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

inline

Definition at line 229 of file differential_transmission.h.

◆ getJointReduction()

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

inline

Definition at line 228 of file differential_transmission.h.

◆ hasActuatorToJointAbsolutePosition()

bool transmission_interface::DifferentialTransmission::hasActuatorToJointAbsolutePosition ( ) const

inlineoverridevirtual

Reimplemented from transmission_interface::Transmission.

Definition at line 224 of file differential_transmission.h.

◆ hasActuatorToJointTorqueSensor()

bool transmission_interface::DifferentialTransmission::hasActuatorToJointTorqueSensor ( ) const

inlineoverridevirtual

Reimplemented from transmission_interface::Transmission.

Definition at line 225 of file differential_transmission.h.

◆ jointToActuatorEffort()

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

inlineoverridevirtual

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 342 of file differential_transmission.h.

◆ jointToActuatorPosition()

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

inlineoverridevirtual

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 368 of file differential_transmission.h.

◆ jointToActuatorVelocity()

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

inlineoverridevirtual

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 355 of file differential_transmission.h.

◆ numActuators()

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

inlineoverridevirtual

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

Implements transmission_interface::Transmission.

Definition at line 222 of file differential_transmission.h.

◆ numJoints()

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

inlineoverridevirtual

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

Implements transmission_interface::Transmission.

Definition at line 223 of file differential_transmission.h.

Member Data Documentation

◆ act_reduction_

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

protected

Definition at line 232 of file differential_transmission.h.

◆ ignore_transmission_for_absolute_encoders_

bool transmission_interface::DifferentialTransmission::ignore_transmission_for_absolute_encoders_

protected

Definition at line 235 of file differential_transmission.h.

◆ jnt_offset_

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

protected

Definition at line 234 of file differential_transmission.h.

◆ jnt_reduction_

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

protected

Definition at line 233 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

◆ DifferentialTransmission() [1/2]

◆ DifferentialTransmission() [2/2]

Member Function Documentation

◆ actuatorToJointAbsolutePosition()

◆ actuatorToJointEffort()

◆ actuatorToJointPosition()

◆ actuatorToJointTorqueSensor()

◆ actuatorToJointVelocity()

◆ getActuatorReduction()

◆ getJointOffset()

◆ getJointReduction()

◆ hasActuatorToJointAbsolutePosition()

◆ hasActuatorToJointTorqueSensor()

◆ jointToActuatorEffort()

◆ jointToActuatorPosition()

◆ jointToActuatorVelocity()

◆ numActuators()

◆ numJoints()

Member Data Documentation

◆ act_reduction_

◆ ignore_transmission_for_absolute_encoders_

◆ jnt_offset_

◆ jnt_reduction_