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

This page is updated frequently. Please
re-visit!

**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.