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Sensorless full body active compliance in a 6 DOF parallel manipulator

Research Project

Project Guide - Mr. Shivesh Kumar, Dr. Arun Dayal Udai, Dr. Suril V Shah

Project Members - Anirvan Dutta, Durgesh Salunkhe

The aim of this research project was to develop a methodology a methodology for sensor-less full body active compliance  on a 6-DOF RSS (Rotary-Spherical-Spherical) parallel manipulator. By using the proposed approach, the manipulator can detect and comply with the external forces on any part of its body without using any explicit force/torque sensor at the joint or the end-effector. This is done by utilizing the estimated joint torque based on the actuator current feedback only. A three-layer cascaded impedance controller for active compliance and reaction to various human interactions are reported. The proposed design and unique methodology for compliance exhibits an effective and inexpensive yet reliable alternative to be used in safe human-robot interactions and force controlled manufacturing applications.


Among the various designs of 6-DOF Parallel Manipulator, we employed 6 - RSS (Rotatory Spherical Spherical) which is commonly known as Zamanov configuration. A 6-DOF manipulator was used with the objective of ultimately providing all the rotational and translation motions to the resulting system. Analytical inverse kinematic solution and loop closure Jacobian was calculated for the designed configuration. This helped in complete inverse dynamic modelling of the platform for compliant control.

After the inverse dynamics is solved, it is critical to interpret the torque values from actuators and implement a control strategy for the compliance. To enable human-robot interaction, it is essential for the parallel manipulator to follow the human intention or comply with the external force. For this a three layer cascaded position based impedance control was utilized. The use of impedance control can be justified in the case of compliance and safety, as when an external force is applied, the end-effector will deviate from its initial pose and follow the desired motion according to the external force. A novel external force (wrench) detection scheme was developed to estimate the external force applied on the manipulator without any explicit sensor.

Screenshot from 2019-08-14 19-06-59.png

A thorough detail of the work can be found on the published paper. A video submission of the compete idea can be found below, as well as the repository can be found in the git active_compliance

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