dynamics_joint/

prismatic.rs

//! Prismatic joint, constraining two objects to translate along a given axis.

use std::fmt::Display;

use dynamics_spatial::{
    configuration::Configuration,
    motion::{SpatialMotion, SpatialRotation},
    se3::SE3,
    vector3d::Vector3D,
};
use rand::rngs::ThreadRng;

use crate::{
    joint::{JointModel, JointType, JointWrapper},
    joint_data::{JointData, JointDataWrapper},
    limits::JointLimits,
};

/// Model of a prismatic joint.
///
/// This joint constraints two objects to translate along a given axis.
#[derive(Clone, Debug)]
pub struct JointModelPrismatic {
    /// The axis of translation expressed in the local frame of the joint.
    pub axis: SpatialMotion,
    /// The joint limits.
    pub limits: JointLimits,
    /// The (null) bias of the joint.
    pub bias: SpatialMotion,
}

impl JointModelPrismatic {
    /// Creates a new `JointModelPrismatic` with the given axis of translation and unbounded limits.
    ///
    /// The axis of translation should be normalized and expressed in the local frame of the joint.
    ///
    /// # Arguments
    ///
    /// * `axis` - The normalized axis of translation expressed in the local frame of the joint.
    ///
    /// # Returns
    /// A new `JointModelPrismatic` object.
    #[must_use]
    pub fn new(axis: Vector3D) -> Self {
        JointModelPrismatic {
            axis: SpatialMotion::from_translational_axis(&axis),
            limits: JointLimits::new_unbounded(1),
            bias: SpatialMotion::zero(),
        }
    }

    /// Creates a new prismatic joint model with `x` as axis of translation.
    ///
    /// # Returns
    /// A new `JointModelPrismatic` object.
    #[must_use]
    pub fn new_px() -> Self {
        Self::new(Vector3D::x())
    }

    /// Creates a new prismatic joint model with `y` as axis of translation.
    ///
    /// # Returns
    /// A new `JointModelPrismatic` object.
    #[must_use]
    pub fn new_py() -> Self {
        Self::new(Vector3D::y())
    }

    /// Creates a new prismatic joint model with `z` as axis of translation.
    ///
    /// # Returns
    /// A new `JointModelPrismatic` object.
    #[must_use]
    pub fn new_pz() -> Self {
        Self::new(Vector3D::z())
    }
}

impl JointModel for JointModelPrismatic {
    fn get_joint_type(&self) -> JointType {
        JointType::Prismatic
    }

    fn nq(&self) -> usize {
        1
    }

    fn nv(&self) -> usize {
        1
    }

    fn neutral(&self) -> Configuration {
        Configuration::from_row_slice(&[0.0])
    }

    fn create_joint_data(&self) -> JointDataWrapper {
        JointDataWrapper::prismatic(JointDataPrismatic::new())
    }

    fn get_axis(&self) -> &SpatialMotion {
        &self.axis
    }

    fn random_configuration(&self, rng: &mut ThreadRng) -> Configuration {
        Configuration::random(
            1,
            rng,
            &self.limits.min_configuration,
            &self.limits.max_configuration,
        )
    }

    fn subspace(&self, v: &Configuration) -> SpatialMotion {
        assert_eq!(
            v.len(),
            1,
            "Prismatic joint model expects a single velocity value."
        );
        SpatialMotion::from_translational_axis(&(v[0] * self.axis.translation()))
    }

    fn subspace_dual(&self, f: &dynamics_spatial::force::SpatialForce) -> Configuration {
        Configuration::from_row_slice(&[f.translation().dot(&self.axis.translation())])
    }

    fn subspace_se3(&self, se3: &SE3) -> SpatialMotion {
        let trans = se3.translation();
        let v = trans.dot(&self.axis.translation()) * self.axis.translation();
        SpatialMotion::from_translational_axis(&v)
    }

    fn bias(&self) -> &SpatialMotion {
        &self.bias
    }

    fn integrate(&self, q: &Configuration, v: &Configuration) -> Configuration {
        Configuration::from_row_slice(&[q[0] + v[0]])
    }
}

impl Display for JointModelPrismatic {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "JointModelPrismatic(axis: {:?})", self.axis.as_slice())
    }
}

/// Data associated to a prismatic joint.
#[derive(Clone, Debug)]
pub struct JointDataPrismatic {
    /// The joint configuration value (translation along the axis).
    pub joint_q: Configuration,
    /// The joint velocity value (velocity along the axis).
    pub joint_v: Configuration,
    /// The placement of the joint in the local frame.
    pub placement: SE3,
    /// The joint velocity as a spatial motion.
    pub joint_velocity: SpatialMotion,
}

impl JointDataPrismatic {
    /// Creates a new `JointDataPrismatic` associated to the given joint model.
    ///
    /// # Arguments
    ///
    /// * `model` - The prismatic joint model.
    ///
    /// # Returns
    /// A new `JointDataPrismatic` object.
    #[must_use]
    pub fn new() -> Self {
        JointDataPrismatic {
            joint_q: Configuration::zeros(1),
            joint_v: Configuration::zeros(1),
            placement: SE3::identity(),
            joint_velocity: SpatialMotion::zero(),
        }
    }
}

impl Default for JointDataPrismatic {
    fn default() -> Self {
        JointDataPrismatic::new()
    }
}

impl JointData for JointDataPrismatic {
    fn get_joint_placement(&self) -> SE3 {
        self.placement
    }

    fn get_joint_q(&self) -> &Configuration {
        &self.joint_q
    }

    fn get_joint_v(&self) -> &Configuration {
        &self.joint_v
    }

    fn update(
        &mut self,
        joint_model: &JointWrapper,
        joint_q: &Configuration,
        joint_v: Option<&Configuration>,
    ) {
        assert_eq!(
            joint_q.len(),
            1,
            "Prismatic joint data update expects a single position value."
        );
        if let Some(joint_v) = joint_v {
            assert_eq!(
                joint_v.len(),
                1,
                "Prismatic joint model expects a single velocity value."
            );
        }

        // store q and v
        self.joint_q = joint_q.clone();
        if let Some(joint_v) = joint_v {
            self.joint_v = joint_v.clone();
            self.joint_velocity = self.joint_v[0] * joint_model.get_axis().clone();
        }

        self.placement = SE3::from_parts(
            joint_model.get_axis().translation() * joint_q[0],
            SpatialRotation::identity(),
        );
    }

    fn get_joint_velocity(&self) -> &SpatialMotion {
        &self.joint_velocity
    }
}