transmission_interface Namespace Reference

Classes
class	ActuatorHandle
class	DifferentialTransmission
class	DifferentialTransmissionLoader
	Class for loading a four-bar linkage transmission instance from configuration data. More...
class	Exception
class	FourBarLinkageTransmission
	Implementation of a four-bar-linkage transmission. More...
class	FourBarLinkageTransmissionLoader
	Class for loading a four-bar linkage transmission instance from configuration data. More...
class	Handle
class	JointHandle
class	SimpleTransmission
class	SimpleTransmissionLoader
	Class for loading a simple transmission instance from configuration data. More...
class	Transmission
	Abstract base class for representing mechanical transmissions. More...
class	TransmissionInterfaceException
class	TransmissionLoader
	Abstract interface for loading transmission instances from configuration data. More...

Typedefs
typedef std::shared_ptr< Transmission >	TransmissionSharedPtr

Functions
template<typename T >
std::string	to_string (const std::vector< T > &list)
template<class T >
std::vector< std::string >	get_names (const std::vector< T > &handles)
template<typename T >
std::vector< T >	get_ordered_handles (const std::vector< T > &unordered_handles, const std::vector< std::string > &names, const std::string &interface_type)
template<class HandleType >
HandleType	get_by_interface (const std::vector< HandleType > &handles, const std::string &interface_name)
template<class T >
bool	are_names_identical (const std::vector< T > &handles)

Variables
constexpr auto	HW_IF_ABSOLUTE_POSITION = "absolute_position"
	Implementation of a differential transmission.

Detailed Description

Author

Adolfo Rodriguez Tsouroukdissian

Variable Documentation

HW_IF_ABSOLUTE_POSITION

constexpr auto transmission_interface::HW_IF_ABSOLUTE_POSITION = "absolute_position"

constexpr

Implementation of a differential transmission.

Implementation of a simple reducer 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.

This transmission relates one actuator and one joint through a reductor (or amplifier). Timing belts and gears are examples of this transmission type, and are illustrated below.

	Effort	Velocity	Position
Actuator to joint	\[ \tau_j = n \tau_a \]	\[ \dot{x}_j = \dot{x}_a / n \]	\[ x_j = x_a / n + x_{off} \]
Joint to actuator	\[ \tau_a = \tau_j / n\]	\[ \dot{x}_a = n \dot{x}_j \]	\[ x_a = n (x_j - x_{off}) \]

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.
• \( n \) is the transmission ratio, and can be computed as the ratio between the output and input pulley radii for the timing belt; or the ratio between output and input teeth for the gear system. The 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. actuator and joint move in opposite directions. For example, in timing belts actuator and joint move in the same direction, while in single-stage gear systems actuator and joint move in opposite directions.