Research Projects of Professor J.W. Grizzle

Current

1. Hybrid Electric Vehicles are vehicles with two or more power sources, such as an internal combustion engine, a battery, and an electric motor. When an HEV is certified for emissions and fuel economy, its power management system must be charge sustaining over the drive cycle, meaning that the battery state of charge (SOC) must be at least as high at the end of the test as it was at the beginning of the test. During the test cycle, the power management system is free to vary the battery SOC so as to minimize a weighted combination of fuel consumption and exhaust emissions. Our work has shown that shortest path stochastic dynamic programming (SP-SDP) offers a more natural formulation of the optimal control problem associated with the design of the power management system because it allows deviations of battery SOC from a desired setpoint to be penalized only at key-off. This method has been illustrated on a parallel hybrid electric truck model that had previously been analyzed using infinite-horizon stochastic dynamic programming with discounted future cost. Both formulations of the optimization problem yield a time-invariant causal state-feedback controller that can be directly implemented on the vehicle. The advantages of the shortest path formulation include that a single tuning parameter is needed to tradeoff fuel economy and emissions versus battery SOC deviation, as compared to two parameters in the discounted, infinite-horizon case, and for the same level of complexity as a discounted future-cost controller, the shortest-path controller demonstrates better fuel and emission minimization while also achieving better SOC control when the vehicle is turned off.

2. Bipedal Robot Locomotion. The motivation for studying walking robots arises from diverse sociological and commercial interests, ranging from the desire to replace humans in hazardous occupations (de-mining, nuclear power plant inspection, military interventions, etc.), to the restoration of motion in the disabled (dynamically-controlled lower-limb prostheses, and FNS/FES), and the appeal of machines that operate in anthropomorphic or animal-like ways (well-known biped and quadruped toys). From a control design perspective, the challenges in legged robots arise from the many degrees of freedom in the mechanisms, the intermittent nature of the contact conditions with the environment, and underactuation. My involvement in this area started during my sabbatical in Strasbourg, from September 1998 through February 1999. My primary interest is in the development of methods to obtain provable motion properties, such as provably asymptotically stable walking and running. My true passion is the nonlinear control theory associated with the project. I am committed to confirming the theory with experiments. In this regard, I have built a new robot, named MABEL.

3. Modeling and Control of Automotive Powertrain Systems. I have been working in this area since 1986, when I was a faculty research scientist at the Scientific Research Laboratory of Ford Motor Company. The overall goal in this project has been to develop, adapt and apply system theoretic notions to the problem of reducing emissions in automobile engines while meeting performance and drivability requirements. The need to satisfy Federal regulations is driving the development of advanced engine technology to meet the ever-increasing demands for lower emissions. These engines are fundamentally described by nonlinear, hybrid (mixed continuous and discrete time) mathematical models, and require sophisticated control systems for their proper functioning. I have partnered with engineers at Ford to construct and validate engine and exhaust system models, and for evaluating modern, model-based feedback design concepts. This is a unique university-industry cooperative research arrangement for developing and applying advanced system theory and control methods to problems important to society.

4. Diabetes Treatment in the ICU. I am working with a diabetologist/endocrinologist to improve the regulation of blood glucose (BG) levels in patients in the intensive care setting, especially those who are there postoperatively. The intense management of diabetes mellitus (DM, or diabetes for short) in the outpatient arena has been a priority for several years, but BG management in the hospital has only recently moved to the forefront. Clinically translating the physiological basis of the side-effects of acute hyperglycemia has only lately occurred, and has shifted the paradigm. Several randomized controlled trials have established the link between glycemic control and improved morbidity and mortality in hospitalized patients, especially in Intensive Care (ICU) settings. Elevated BG levels are found in ICU patients with and without a known history of diabetes. Since known diabetes is a co-morbid condition in 30-40 % of hospitalized patients, addition of stress-induced hyperglycemia (SIH) to the picture is increasing BG management in an ICU to an epidemic proportion. Hospitals around the country and the world now recognize BG as a modifiable risk factor. The goals of the project are
   1. Perform an extensive control analysis of the University of Michigan insulin infusion protocol in closed-loop with a validated dynamic model of the class of patients seen in the ICU. We will study its nominal response and its response to a wide range of model parameter variations. From this, we will predict the fraction of patients the protocol will maintain within a given goal range.
   2. Perform a similar analysis for protocols from other hospitals.
   3. On the basis of the model building and closed-loop control analysis performed above, we will propose improvements to the University of Michigan's protocol.
   For me, this area is brand new. Several other control specialists work in this area, including Frank Doyle, Roman Hovorka, Clyde Martin, and Dale Seborg.

5. Nonlinear Control. My primary research area used to be the theory of nonlinear control systems. My work now has a more applied focus emphasizing the modeling and control of automotive powertrain systems and bipedal robots. The models encountered in these subjects are more often than not nonlinear, and hence nonlinear control plays a big role in arriving at solutions to these problems. The big difference with my previous work is that now the questions I pose are based in practical engineering systems. Before, I could modify my hypotheses to arrive at a beautiful theorem, whereas now, reality is what it is, and I am challenged to discover the right control method for the problem at hand.

   Less Current

6. Rehabilitation Robotics. Assisting the human body in the recovery of locomotor ability requires a multidisciplinary perspective. Our research team involved five faculty members, one each from Kinesiology (Ferris), Mechanical Engineering (Gillepsie), and Neurology (Aldridge), and two from Electrical Engineering and Computer Science (Koditschek and Grizzle).
7. Microelectronics Manufacturing. [My current activity in this area is extremely minimal.] This was a very multidisciplinary project! It involved a team of faculty from control systems, solid state physics and electromagnetics working to reduce variability and increase precision in standard semiconductor manufacturing processes. Our work encompassed both sensor development and algorithm development for real-time process control. Our primary research vehicle was the etch of 0.1 micron gate structure, on a Lam 9400.