differential_transmission.h

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// Copyright (C) 2013, PAL Robotics S.L.
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#ifndef TRANSMISSION_INTERFACE_DIFFERENTIAL_TRANSMISSION_H
#define TRANSMISSION_INTERFACE_DIFFERENTIAL_TRANSMISSION_H

#include <cassert>
#include <string>
#include <vector>

#include <transmission_interface/transmission.h>
#include <transmission_interface/transmission_interface_exception.h>

namespace transmission_interface
{

class DifferentialTransmission : public Transmission
{
public:
  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));

  void actuatorToJointEffort(const ActuatorData& act_data,
                                   JointData&    jnt_data);

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

  void actuatorToJointPosition(const ActuatorData& act_data,
                                     JointData&    jnt_data);

  void jointToActuatorEffort(const JointData&    jnt_data,
                                   ActuatorData& act_data);

  void jointToActuatorVelocity(const JointData&    jnt_data,
                                     ActuatorData& act_data);

  void jointToActuatorPosition(const JointData&    jnt_data,
                                     ActuatorData& act_data);

  std::size_t numActuators() const {return 2;}
  std::size_t numJoints()    const {return 2;}

  const std::vector<double>& getActuatorReduction() const {return act_reduction_;}
  const std::vector<double>& getJointReduction()    const {return jnt_reduction_;}
  const std::vector<double>& getJointOffset()       const {return jnt_offset_;}

protected:
  std::vector<double>  act_reduction_;
  std::vector<double>  jnt_reduction_;
  std::vector<double>  jnt_offset_;
};

inline DifferentialTransmission::DifferentialTransmission(const std::vector<double>& actuator_reduction,
                                                          const std::vector<double>& joint_reduction,
                                                          const std::vector<double>& joint_offset)
  : Transmission(),
    act_reduction_(actuator_reduction),
    jnt_reduction_(joint_reduction),
    jnt_offset_(joint_offset)
{
  if (numActuators() != act_reduction_.size() ||
      numJoints()    != jnt_reduction_.size() ||
      numJoints()    != jnt_offset_.size())
  {
    throw TransmissionInterfaceException("Reduction and offset vectors of a differential transmission must have size 2.");
  }

  if (0.0 == act_reduction_[0] ||
      0.0 == act_reduction_[1] ||
      0.0 == jnt_reduction_[0] ||
      0.0 == jnt_reduction_[1]
  )
  {
    throw TransmissionInterfaceException("Transmission reduction ratios cannot be zero.");
  }
}

inline void DifferentialTransmission::actuatorToJointEffort(const ActuatorData& act_data,
                                                                  JointData&    jnt_data)
{
  assert(numActuators() == act_data.effort.size() && numJoints() == jnt_data.effort.size());
  assert(act_data.effort[0] && act_data.effort[1] && jnt_data.effort[0] && jnt_data.effort[1]);

  std::vector<double>& ar = act_reduction_;
  std::vector<double>& jr = jnt_reduction_;

  *jnt_data.effort[0] = jr[0] * (*act_data.effort[0] * ar[0] + *act_data.effort[1] * ar[1]);
  *jnt_data.effort[1] = jr[1] * (*act_data.effort[0] * ar[0] - *act_data.effort[1] * ar[1]);
}

inline void DifferentialTransmission::actuatorToJointVelocity(const ActuatorData& act_data,
                                                                    JointData&    jnt_data)
{
  assert(numActuators() == act_data.velocity.size() && numJoints() == jnt_data.velocity.size());
  assert(act_data.velocity[0] && act_data.velocity[1] && jnt_data.velocity[0] && jnt_data.velocity[1]);

  std::vector<double>& ar = act_reduction_;
  std::vector<double>& jr = jnt_reduction_;

  *jnt_data.velocity[0] = (*act_data.velocity[0] / ar[0] + *act_data.velocity[1] / ar[1]) / (2.0 * jr[0]);
  *jnt_data.velocity[1] = (*act_data.velocity[0] / ar[0] - *act_data.velocity[1] / ar[1]) / (2.0 * jr[1]);
}

inline void DifferentialTransmission::actuatorToJointPosition(const ActuatorData& act_data,
                                                                    JointData&    jnt_data)
{
  assert(numActuators() == act_data.position.size() && numJoints() == jnt_data.position.size());
  assert(act_data.position[0] && act_data.position[1] && jnt_data.position[0] && jnt_data.position[1]);

  std::vector<double>& ar = act_reduction_;
  std::vector<double>& jr = jnt_reduction_;

  *jnt_data.position[0] = (*act_data.position[0] / ar[0] + *act_data.position[1] / ar[1]) / (2.0 * jr[0]) + jnt_offset_[0];
  *jnt_data.position[1] = (*act_data.position[0] / ar[0] - *act_data.position[1] / ar[1]) / (2.0 * jr[1]) + jnt_offset_[1];
}

inline void DifferentialTransmission::jointToActuatorEffort(const JointData&    jnt_data,
                                                                  ActuatorData& act_data)
{
  assert(numActuators() == act_data.effort.size() && numJoints() == jnt_data.effort.size());
  assert(act_data.effort[0] && act_data.effort[1] && jnt_data.effort[0] && jnt_data.effort[1]);

  std::vector<double>& ar = act_reduction_;
  std::vector<double>& jr = jnt_reduction_;

  *act_data.effort[0] = (*jnt_data.effort[0] / jr[0] + *jnt_data.effort[1] / jr[1]) / (2.0 * ar[0]);
  *act_data.effort[1] = (*jnt_data.effort[0] / jr[0] - *jnt_data.effort[1] / jr[1]) / (2.0 * ar[1]);
}

inline void DifferentialTransmission::jointToActuatorVelocity(const JointData&    jnt_data,
                                                                    ActuatorData& act_data)
{
  assert(numActuators() == act_data.velocity.size() && numJoints() == jnt_data.velocity.size());
  assert(act_data.velocity[0] && act_data.velocity[1] && jnt_data.velocity[0] && jnt_data.velocity[1]);

  std::vector<double>& ar = act_reduction_;
  std::vector<double>& jr = jnt_reduction_;

  *act_data.velocity[0] = (*jnt_data.velocity[0] * jr[0] + *jnt_data.velocity[1] * jr[1]) * ar[0];
  *act_data.velocity[1] = (*jnt_data.velocity[0] * jr[0] - *jnt_data.velocity[1] * jr[1]) * ar[1];
}

inline void DifferentialTransmission::jointToActuatorPosition(const JointData&    jnt_data,
                                                                    ActuatorData& act_data)
{
  assert(numActuators() == act_data.position.size() && numJoints() == jnt_data.position.size());
  assert(act_data.position[0] && act_data.position[1] && jnt_data.position[0] && jnt_data.position[1]);

  std::vector<double>& ar = act_reduction_;
  std::vector<double>& jr = jnt_reduction_;

  double jnt_pos_off[2] = {*jnt_data.position[0] - jnt_offset_[0], *jnt_data.position[1] - jnt_offset_[1]};

  *act_data.position[0] = (jnt_pos_off[0] * jr[0] + jnt_pos_off[1] * jr[1]) * ar[0];
  *act_data.position[1] = (jnt_pos_off[0] * jr[0] - jnt_pos_off[1] * jr[1]) * ar[1];
}

} // transmission_interface

#endif // TRANSMISSION_INTERFACE_DIFFERENTIAL_TRANSMISSION_H