Trajectory_control

This paper presents a new controller for parallel robots. The design of the controller is based on the dynamic robot model, and it uses Linear Algebra Theory and Numerical Methods. The controller stability analysis demonstrates that it is globally uniformly asymptotically stable. Simulations and experimental results with an actual 3UPS+RPU parallel robot confirm the feasibility and the effectiveness of the proposed controller. The new strategy allows an intuitive adjustment of parameters, the computational cost is low, and the robot is able to follow the trajectory references closely.

This video shows the execution of a trajectory generated by Dynamic Movement Primitives (DMP) to simultaneously provide an admittance behavior and avoid Type II singular configurations for the 4-DOF parallel robot. The trajectory is modified by one coupling action defined for the human-robot admittance interaction and another for the singularity avoidance.

A compliant-admittance controller complemented with a Type II evader module is implemented on a 4-DOF parallel robot. The Type II singularity evader provides complete user control over the robot because the evader modifies online the actuators’ trajectory if a singularity is close. The proximity to a singularity is measured by the minimum angle Ω. The location of the actuator on limb 3 is presented to verify the activation of the evader module, while the robot's location on z_m measured by a 3D tracking system demonstrates the complete control over the robot.

A raw compliant-admittance controller implemented on a 4-DOF parallel robot. The video shows how the user drives the robot to a Type II singularity and loses control with a final fall of the robot. The proximity to a singularity is measured by the determinant of the forward Jacobian (‖J_D ‖) and the minimum angle Ω. The robot's location on z_m, measured by a 3D tracking system, verifies the robot's fall. In the figures, the subindex “a” represents the admittance reference, the subindex “c” stands for measurements, and the “lim” represents the experimental limits.

A compliant-admittance controller complemented with a Type II evader module is implemented on a 4-DOF parallel robot and tested with a patient. The Type II singularity evader provides complete user control over the robot because the evader modifies online the actuators’ trajectory if a singularity is close. The proximity to a singularity is measured by the minimum angle Ω.

This video shows the execution of a trajectory generated by Dynamic Movement Primitives (DMP) to provide an admittance behavior for the 4-DOF parallel robot. A coupling action is defined as the difference between a reference force and the exerted force, and this coupling action is fed to the DMP to allow the compliant manipulation.

This video shows the execution of a trajectory generated by Dynamic Movement Primitives (DMP) to avoid Type II singular configurations for the 4-DOF parallel robot. To this end, an initial singular trajectory is encoded by the DMP, which is modified during execution by using coupling actions.

Hybrid control: identification of two parameters (high-speed, high-resolution video summary)

This video shows the execution of a new controller for the 4dof parallel robot. It is a hybrid controller that uses window-based least (WLS)
squares or recursive least squares (RLS) for the identification of the robot’s parameters. In this case, by means RLS we estimate the first
and second relevant parameters. The first relevant parameter corresponds basically to the mobile platform mass and the second relevant parameter
represent the first inertia moment on X axis of the limb 1.

In order to verify the developed controller, some experiments have been carried out. For these experiments, the trajectories employed involve
sinusoidal movements around the generalized coordinates (x, z, θ, ψ), wich sntail two hip flexion combined with flexion-extension of knee.
Four pauses are introduced where the robot maintains the mobile platform horizontally in a fixed position, waiting for a payload to be placed
(or removed) during 20 seconds. Starting with no payload (stage 1), a 25 kg payload is placed at instant t=100 s (stage 2) and moved away
at t=220 s (stage 3). Afterwards, a 15 kg payload is placed at t=340 s (stage 4) and removed at instant t=460 s (stage 5).

Hybrid control: identification of one parameter (high-speed, high-resolution video summary)

This video shows the execution of a new controller for the 4dof parallel robot. It is a hybrid controller that uses window-based least (WLS)
squares or recursive least squares (RLS) for the identification of the robot’s parameters. In this case, by means RLS we estimate the first
relevant parameter that basically corresponds with the mobile platform mass.

In order to verify the developed controller, some experiments have been carried out. For these experiments, the trajectories employed involve
sinusoidal movements around the generalized coordinates (x, z, θ, ψ), wich sntail two hip flexion combined with flexion-extension of knee.
Four pauses are introduced where the robot maintains the mobile platform horizontally in a fixed position, waiting for a payload to be placed
(or removed) during 20 seconds. Starting with no payload (stage 1), a 25 kg payload is placed at instant t=100 s (stage 2) and moved away
at t=220 s (stage 3). Afterwards, a 15 kg payload is placed at t=340 s (stage 4) and removed at instant t=460 s (stage 5).

This video shows the execution of a new controller for the 4dof parallel robot. It is a hybrid controller that uses window-based least squares and recursive least squares for the identification of the robot’s parameters. In this case, we estimate the first relevant parameter that basically corresponds with the mobile platform mass.

In order to verify the developed controller, some experiments have been carried out. For these experiments, the trajectories employed involve sinusoidal movements around the generalized coordinates (x, z, θ, ψ). Four pauses are introduced where the robot maintains the mobile platform horizontally in a fixed position, waiting for a payload to be placed (or removed) during 20 seconds. Starting with no payload (stage 1), a 25 kg payload is placed at instant t=100 s (stage 2) and moved away at t=220 s (stage 3). Afterwards, a 15 kg payload is placed at t=340 s (stage 4) and removed at instant t=460 s (stage 5).