Does PD Control Always Work for Robotic Systems? by Dr Shishir N Y Kolathaya

Location: CSA Seminar Hall (Room No. 254, First Floor)

Speaker : Dr Shishir N Y Kolathaya,
INSPIRE Faculty Fellow, RBCCPS, IISc

Title : Does PD Control Always Work for Robotic Systems?

Date : Tuesday, October 22, 2019

Time : 11:00 AM

Venue : CSA Seminar Hall (Room No. 254, First Floor)

Abstract

In 2015, a committee created by the International Federation of Automatic Control (IFAC) surveyed its members to obtain their views on the impact of advanced control in industries. PID control was first with a 100% high-impact rating, and nonlinear control was tenth with a 22% rating. Clearly, despite great advances in the theory of nonlinear controls,PD and PID tracking control laws continue to be the  host popular choice. This is true even for robotic systems. Therefore, the goal of the talk is to understand some of the stability guarantees provided by PD control laws in the context of robotic systems.

The talk is divided into two parts. First, we will discuss existing stability results for PD controlled robotic systems. Some of these results were established as early as the 1980’s. Second, we will extend these stability properties to underactuated and hybrid robotic systems i.e., by introducing additional assumptions on the unactuated coordinates of the robot. We will demonstrate these results on bipedal walking robots, which are known to be textbook examples for hybrid robotic systems. Bipedal robots have the leg-swing as the continuous event, and the foot-strike as the discrete event, and these events alternate during walking. In addition, bipeds largely have underactuations due to the interactions between feet and ground. For each continuous event, we establish that the convergence rate of the tracking error can be regulated via appropriate tuning of the PD gains, and for each discrete event, we establish that this convergence rate sufficiently overcomes the nonlinear impacts by assumptions on the hybrid zero dynamics. Towards the end, we will validate these results on a 5-link bipedal walker in simulation.

Biography of the speaker

Shishir is an INSPIRE Faculty fellow in the Robert Bosch Center for Cyber Physical Systems (RBCCPS) in IISc Bangalore. He received his Ph.D. degree in Mechanical Engineering (2016) from the Georgia Institute of Technology, M.S. degree in Electrical Engineering (2012) from Texas A&M University, and B.Tech degree in Electrical & Electronics Engineering (2008) from National Institute of Technology Karnataka. His primary focus as a Ph.D. student was on stability and control of walking robots. Shishir is currently interested in safety-critical control, stability of hybrid systems, and deep reinforcement learning for all kinds of robotic platforms.

Host Faculty : Prof. Matthew Jacob