Kevin C. Craig

Mechatronic design of a ball-on-plate balancing system

This paper discusses the conception and development of a ball-on-plate balancing system based on mechatronic design principles. Realization of the design is achieved with the simultaneous consideration towards constraints like cost, performance, functionality, extendibility, and educational merit. A complete dynamic system investigation for the ball-on-plate system is presented in this paper. This includes hardware design, sensor and actuator selection, system modeling, parameter identification, controller design and experimental testing. The system was designed and built by students as part of the course Mechatronics System Design at Rensselaer.

Granular collision lubrication

The flow of powder or granules has been proposed as a mechanism of lubrication suitable for high‐temperature applications where conventional liquid lubrication fails. This study is primarily experimental with a simplified theory presented for interpreting the data. Two key features are present which seem to be additive: (1) a collisional normal stress generated by kinetic energy of the particles, and (2) a lubrication normal stress due to converging surfaces. Experiments are conducted in an annular shear cell with sliding motion between opposing surfaces. The shear surface may be flat or contain three sloping regions with a step. Normal stress (load) and shear stress (friction) are proportional to shear rate squared. In the case of inclined surfaces, stresses are also proportional to the surface slope squared.

Inverted pendulum systems: Rotary and arm-driven - A mechatronic system design case study

The inverted pendulum, a popular mechatronic application, exists in many different forms. The common thread among these systems is to balance a link on end using feedback control. Two challenging inverted pendulum systems are the rotational and arm-driven systems. The system described in this paper can be transformed from the rotational to the arm-driven configuration by replacing the links and setting the base on its side. It was designed and built by students as part of the course Mechatronic System Design at Rensselaer. This paper presents a summary of a mechatronic system design case study for the rotary inverted pendulum system.

Robust, digital, nonlinear control of magnetic-levitation systems

This paper presents a robust, adaptive, nonlinear controller for a class of magnetic-levitation systems, which includes active-magnetic bearings. The controller is analytically and experimentally shown to be superior to a classical linear control system in stability, control effort, step-response performance, robustness to parameter variations, and force-disturbance rejection performance, Using an adaptive backstepping approach, a Lyapunov function is generated along with an adaptive control law such that the nonlinear, closed-loop, continuous system is shown to guarantee stability of the equilibrium and convergence of the parameter estimates to constant values. The control system error coordinates are proven to be bounded in the presence of a bounded force disturbance input. The novelty of this controller is that it is digitally implemented using Euler integrators with anti-windup limits, it is single-input-single-output requiring only a measurement of the position of the levitating object, and it is designed to adaptively estimate not only the uncertain model parameters, but also the constant forces applied to the levitating object in order to ensure robustness to force disturbances. The experimental study was conducted on a single-axis magnetic-levitation device. The controller is shown to be applicable to active-magnetic bearings, under specific conditions, as well as any magnetic-levitation system that can be represented in output-feedback form.

Is anything really new in mechatronics education

Yes, there is something new in the way mechanical engineers are expected to design and in the way professors must now teach design. To illustrate how one institution is helping mechanical engineers to become mechatronics engineers, the article describes the undergraduate program in mechatronics at Rensselaer Polytechnic Institute, and in particular, the integration of the theory covered in lectures with the laboratory exercises. The hardware systems used in both courses are described. Also discussed are observations from conducting professional training in mechatronics both in industry and for the ASME Professional Development Program.

Design of flexible rods with embedded SMA actuators

The shape change of a stress free cylindrical flexible rod with embedded SMA actuators is modeled in this paper for rods with single or multiple SMA actuators placed parallel to the long axis of the rod for the first heating of the SMA actuators. The deformed shape of the rod is found by solving the nonlinear equations of equilibrium of the rod. For multiple actuators the resultant forces and moments are considered. A design analysis is performed for the active rod with a single SMA actuator. Key design variables are: EROD, the thermal bond strength of the rod to the SMA actuator, and the rod dimensions. Key design parameters are: maximum rod/actuator interfacial shear stress, rod strain, rod slenderness ratio, and rod deflection. An analysis is then performed which investigates the influence of the design variables on each of the design parameters. Optimal values are obtained which yield desired design parameter values. Experimental prototypes are fabricated, tested, and the deformed shape is compared to the theoretical prediction.

Use of FEA Derived Impedances to Design Active Structures

Previously, the impedance method has been applied to simple structures by determining the modal response using closed-form methods. The present work uses finite element analysis (FEA) to generate the host structure’s mechanical impedances from eigenvectors. Two-dimensional structures are studied, though the method should be extendable to any structure that can be modeled by FEA. The equations to recover the impedances and structure’s response from an FEA normal mode analysis are developed. The method is then experimentally verified for plates with different boundary conditions, material types, and actuator orientations. The method is found to accurately predict the plate’s response.

The role of computers in mechatronics

The author examines the role computers hold in the field of mechatronics, and what educators need to focus on for all engineering students, not just mechanical engineering students.

Design, Construction and Testing of a Single-axis Servomechanism for Control Experiments involving Coulomb Friction, Backlash and Joint Compliance

SUMMARY An investigation of the effects of system non-linearities, such as Coulomb friction and backlash, and undesirable structural dynamics, such as joint compliance, on the dynamic modeling and control of mechanical positioning systems is presented. These effects are often neglected in dynamic system analysis and control studies. An innovative, computer-controlled, mechanical positioning test bed was designed and constructed to facilitate investigations of these effects. The test bed allows fully adjustable, quantified and well-defined measurements of Coulomb friction, backlash, joint compliance and inertia. System identification and parameter estimation techniques are used to estimate and verify linear system parameters. Open-loop and closed-loop simulations of the system, incorporating the undesirable effects which can be exhibited by the test bed, are presented and compared with experimental results. The positioning performance of the servomechanism is shown to degrade with increases in Coulomb fric...

Incorporating finite element techniques to simplify the impedance modeling of active structures

An impedance model is formulated for the prediction of the response of structures to induced-strain actuation. The approach utilizes finite element analysis (FEA) to determine the host- structure mechanical impedance. The method couples the numerically obtained impedance to an analytical vibration solution of the induced-strain actuator to determine the dynamic response of the active structure. The methodology is demonstrated in the computation of the dynamic response of a beam structure to induced-strain actuation. This system has been extensively explored by the active structures community. Comparisons of the predicted dynamic response of this structure are made to the predictions of models previously documented in the literature. Experiments are conducted for the purpose of model validation, and an excellent agreement is demonstrated between the predictions of the FEA-based impedance model and measurements made on physical systems. It is anticipated that the formulation extends the FEA-based impedance modeling approach to a broader class of active structures, those for which closed-form expressions of host-structure mechanical impedance are non- existent. Use of the FEA-based impedance approach is suggested when modeling generic distributed structures possessing material anisotropy, mass loading, and non-uniform boundary conditions.