Robotics, Control and Mechatronics Laboratory

Dr. Hanz Richter, Mechanical Engineering Department, Cleveland State University

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Current Projects:

Optimal prosthesis design with energy regeneration (link to Simon Embedded Lab)
Funding from the National Science Foundation (Simon PI, Richter and van den Bogert co-PIs), 2013-2017

Control and Optimization of Robots with Energy Regeneration:

Funding from the National Science Foundation (Richter PI), 2015-2018

This research will introduce a systematic treatment of general motion control problems with explicit consideration of bidirectional energy flow. The intellectual significance of the project is centered in its generality and broad applicability, which contrasts with the mostly case-oriented current literature on regenerative systems. The project focuses on the use of ultracapacitors as key elements of advanced regenerative systems. In comparison to batteries, ultracapacitors have very high power densities. This means that energy extraction and return can be achieved at fast rates. This feature affords great flexibility to alter a robot's dynamic behavior by means of control, in particular its mechanical impedance. Moreover, recent advances in graphene-based ultracapacitors have resulted in devices with energy densities approaching those of lithium-ion batteries. These advances have the potential for the elimination of batteries in certain mobile robotic systems, particularly in medical assistive devices. The project will establish a framework to design, control and optimize such systems. The project has three goals: 1. development of new approaches for modeling, control and design of robotic systems with advanced regenerative hardware such as ultracapacitors; 2. formulation and solution of fundamental energy-motion multi-objective optimization problems for the same; 3. bridging of theory and practice with a custom-built study robot.

Cyber-Enabled Exercise Machines:
Funding from the National Science Foundation (Richter PI, Simon, Sparks and van den Bogert, co-PIs), 2015-2019

This research will contribute to the foundations of cyber-physical system science in the following aspects: biomechanical modeling and real-time musculoskeletal state estimation; estimation theory and unscented H-infinity estimation; control theory and human-machine interaction dynamics, and micro-evolutionary optimization for real-time systems. The proposed Cyber-Enabled Exercise Machines (CEEMs) are highly reconfigurable devices which adapt to the user in pursuit of an optimization objective, namely maximal activation of target muscle groups. Machine adaptation occurs through port impedance modulation, and optimal cues are generated for the exerciser to follow. The goals of the project are threefold: i) development of foundational cyber-physical science and technology in the field of human-machine systems; ii) development of new approaches to modeling, design, control and optimization of advanced exercise machines, and iii) application of the above results to develop two custom-built CEEMs: a rowing ergometer and a 2-degree-of-freedom resistance machine.

Past Projects:

Development of a leg prosthesis test robot
Funding from the Cleveland Clinic Foundation and the State of Ohio 2012-2014

Pilot Studies for a Rowing Ergometer with Energy Regeneration (tech report)
Funding from ZIN Technologies and NASA Glenn Research Center 2014-2015

Multiplexed Implementation of Model-Predictive Control for Aircraft Engines
Funding from NASA Glenn Research Center

In this project, we investigate ways to reduce the computational complexity of model predictive control, so that implementation is feasible in real-time, using aircraft onboard processing. We demonstrated the feasibility of introducing a cyclic sequence for actuator updates within the framework of MPC. By doing this, the quadratic program that must be solved at each sampling interval is reduced to a one-degree-of-freedom search (corresponding to the actuator being updated). Since quadratic programs have a complexity that grows with the cube of the number of controls being optimized, substantial computation savings are obtained. We demonstrated that the speed of computation could be easily doubled without significant performance losses. We provided analytical results concerning the effects of multiplexing in a system, including the use of observers.

Set Invariance Methods for Constrained Variable-Structure Control

This control-theoretical effort incorporates set invariance concepts in the area of variable-structure control, with the aim of designing controllers which guarantee safe operation in the presence of state and control constraints and uncertainties. The theory allows a designer to specify a sliding-mode controller which is guaranteed to keep the system within the boundaries of an invariant set which results from the intersection of a cylinder and the state constraints. A designer computes the control gains and invariant sets by solving a Linear Matrix Inequality (LMI). Current results are being applied to two problems: optimal transfer of liquid containers with slosh constraints and to hybrid controls of rotorcraft drivetrains (NASA Glenn).

Control of Smart Structures with Limited Hardware
Piezoelectric actuators have been successfully used in vibration control, high-precision positioning and shape control. In systems requiring large numbers of actuators (multi degree-of-freedom space structures), the cost and bulk of the power amplifiers becomes a limitation. In this research we explore the idea of sharing a reduced number of power units among the actuators according to some schedule, for instance multiplexing. Preliminary work suggests that it might be possible, for example, to simultaneously stabilize two cantilever beams with just one amplifier, by following a multiplexing arrangement. Theory has been developed by lab members to design linear controllers that operate under multiplexing and guarantee stable operation. This theory is being applied to an experimental setup consisting of an array of beams to be simultaneously stabilized. This research also extends the multiplexing approach to arbitrary switching among the amplifiers, piezo patches and passive shunts. Hybrid dynamical theory is being used as a framework.

Strain-Sensing with Piezoelectric Biopolymers
In this project, we investigate the potential uses of certain piezoelectric biopolymers as biomedical sensors. Many biopolymers such as collagen, chitin and cellulose are known to exhibit piezoelectric activity. Some of these materials are already being used in biomedical applications for surgical threads and wound dressings, due to their excellent mechanical properties and biocompatibility. In this project we consider exploiting their piezoelectric activity to create biocompatible sensors. We collaborate with the CSU Physics Dept. in depositing thin metallic layers on biopolymer strips to create electrodes.

Attitude Control with Cold-Gas Thrusters
The focus of this project is to develop robust ON-OFF strategies for rotational attitude control of small satellites using cold-gas thrusters. We built a testbed consisting of a rotating platform propelled by Nitrogen from a high-pressure tank. A basic time-fuel optimal law was implemented in the system with good results. Many issues remain regarding the robustness of the control law and the number of firings. According to time-optimal theory, at most two firings should occur in a time-optimal law for the double integrator. But in practice, chattering of the solenoid valves is observed, especially near the target attitude. Existing theory has limitations which make it inapplicable when severe uncertainty is present (Jing and McInnes, Automatica, 2002). We are seeking to develop an improved strategy aimed at the elimination of chattering when severe uncertainties influence system behavior.