Stiff and safe task-space position and attitude controller for robotic manipulators

Gyuho Byun,Ryo Kikuuwe

doi:10.1186/s40648-020-00166-1

Gyuho Byun, Ryo Kikuuwe

Open Access

https://doi.org/10.1186/s40648-020-00166-1

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Journal: ROBOMECH Journal	Publication Date: Mar 30, 2020
Citations: 2	License type: open-access

Affiliation: Hiroshima University, Kyushu University

Abstract

This paper proposes a stiff and safe task-space position and attitude control scheme for robotic manipulators. This study extends the work of Kikuuwe et al’s. (2006) velocity-bounding proxy-based sliding mode control by explicitly addressing the attitude part. The proposed controller has a Jacobian-based structure, which realizes smooth trajectories when the desired attitude is far rotated from the actual attitude. It also imposes arbitrary magnitude limits on the end-effector velocity, angular velocity, and each actuator force without sacrificing a stiffness, which is the same level as a high-gain PID position control below the limits. The benefit of the proposed controller becomes apparent after the robot yields to external forces due to force saturations, when the robot makes contact with obstacles. In such a situation, if the external forces disappear, the controller generates overdamped resuming motion from large tracking errors. The proposed controller can be expected to enhance the safety of robotic applications for the human–robot interaction. The proposed method is validated by experiments employing a six-degree of freedom industrial manipulator.

Highlights

When the robotic manipulators work in three dimensional task space, the robot’s trajectory is usually described by task-space coordinate vectors that contain a position vector and attitude of the robot end-effector
This paper proposes a stiff and safe task-space controller for robotic manipulators, which is an extension of velocity bounding PSMC (VBPSMC) with addressing the attitude part using the unit quaternion
Task‐space controller This paper considers a torque-commanded manipulator having six-degrees-of-freedom, which can be described in the following form: M(qs)qs = τ c + τ g + h + d where M(qs) ∈ R6×6 denotes a symmetric positive-definite matrix that represents the inertia, τ g ∈ R6 denotes gravity compensation torques, τ c ∈ R6 represents actuator force generated from the output of the controller, h ∈ R6 denotes forces applied to the object from external forces and d ∈ R6 denotes the sum of forces resulted from all unmodeled factors

Summary

Introduction

When the robotic manipulators work in three dimensional task space, the robot’s trajectory is usually described by task-space coordinate vectors that contain a position vector and attitude of the robot end-effector. The proposed controller has a Jacobian-based structure, which does not produce excessively large speed in the vicinity of singular configurations It imposes arbitrary magnitude limits on the end-effector velocity, angular velocity and each actuator force without sacrificing its stiffness, which is the same level as a high-gain PID position control below the limits. If the external forces disappear, the controller generates overdamped resuming motion from the large tracking errors This behavior looks similar to the compliant behavior that is realized by an impedance control for the robotic manipulators [24,25,26], but its tracking accuracy is the same level as the high-gain PID position control during normal operation.

Background

Conclusion