Nonlinear control of mechatronic systems with permanent-magnet DC motors

The current trends in development and deployment of advanced electromechanical systems have facilitated the unified activities in the analysis and design of state-of-the-art motion devices, electric motors, power electronics, and digital controllers. This paper attacks the motion control problem (stabilization, tracking, and disturbance attenuation) for mechatronic systems which include permanent-magnet DC motors, power circuity, and motion controllers. By using an explicit representation of nonlinear dynamics of motors and switching converters, we approach and solve analysis and control problems to ensure a spectrum of performance objectives imposed on advanced mechatronic systems. The maximum allowable magnitude of the applied armature voltage is rated, the currents are limited, and there exist the lower and upper limits of the duty ratio of converters. To approach design tradeoffs and analyze performance (accuracy, settling time, overshoot, stability margins, and other quantities), the imposed constraints, model nonlinearities, and parameter variations are thoroughly studied in this paper. Our goal is to attain the specified characteristics and avoid deficiencies associated with linear formulation. To solve these problems, an innovative controller is synthesized to ensure performance improvements, robust tracking, and disturbance rejection. One cannot neglect constraints, and a bounded control law is designed to improve performance and guarantee robust stability. The offered approach uses a complete nonlinear mechatronic system dynamics with parameter variations, and this avenue allows one to avoid the conservative results associated with linear concept when mechatronic system dynamics is mapped by a linear constant-coefficient differential equation. To illustrate the reported framework and to validate the controller, analytical and experimental results are presented and discussed. In particular, comprehensive analysis and design with experimental verification are performed for an electric drive. A nonlinear bounded controller is designed, implemented, and experimentally tested.     

Hierarchical optimal contour control of motion systems

Many motion control applications utilize multiple axes to traverse complex trajectories. The hierarchical contour control methodology proposed in this paper treats each axis as an individual subsystem and combines the Internal Model Principle with robust tracking and optimal hierarchical control techniques to track a desired trajectory. In this method the objectives are divided into two levels. Measurable goals of each subsystem are included in the bottom level and unmeasurable goals, which are estimated using the bottom level states, are considered in the top level where the subsystems are synchronized. The proposed methodology reduces system complexity while greatly improving tracking performance. The tracking error for each axis is considered in the bottom level where the Internal Model Principle is used to compensate for unmodeled nonlinear friction and slowly varying uncertainties. The top level goal (i.e., zero contour error) is propagated to the lower level by an aggregation relationship between contour error and physical linear axis variables. A controller is designed at the bottom level which simultaneously satisfies the bottom level goals (i.e., individual axis tracking) and the top level goal. Experimental results implemented on a table top CNC machine for diamond and freeform contours illustrate the performance of the proposed methodology. While this methodology was implemented for a two-axis motion system, it can be extended to any motion system containing more than two axes.     

Telescopes as mechatronic systems

The system design of telescopes is usually dominated by the aspects of the optics and receiving instruments. The telescope structure, mechanism, and control are "only" aids to position these elements toward the celestial target, but their quality has a big impact on the final performance. This paper describes an integrated design approach to these "mechatronic" telescope subsystems.     

Thermoelectric modules in mechatronic systems: Temperature-dependent modeling and control

Active thermal control is crucial in achieving the required accuracy and throughput in many industrial applications, e.g., in the medical, high-power lighting, and semiconductor industry. Thermoelectric Modules (TEMs) can be used to both heat and cool, alleviating some of the challenges associated with traditional electric heater based control. However, the dynamic behavior of these modules is non-affine in their inputs and state, complicating their implementation. To facilitate advanced control approaches a high fidelity model is required. In this paper an approach is presented that increases the modeling accuracy by incorporating temperature-dependent parameters. Using an experimental identification procedure, the parameters are estimated under different operating conditions. The resulting model is used in a feedback linearization approach to linearize the system, facilitating the use of advanced linear control techniques. Moreover, it presents an observer based approach to reconstruct state information in cases where sensor placement is limited. The resulting framework forms a complete approach to temperature-dependent modeling and control of thermoelectric elements.     

Integrated structure and control design for mechatronic systems with configuration-dependent dynamics

This paper considers the optimal design of mechatronic systems with configuration-dependent dynamics. An optimal mechatronic design requires that, among the structural and control parameters, an optimal choice has to be made with respect to design specifications in the different domains. Two main challenges are treated in this paper: the non-convex nature of the optimization problem and the difficulty in modeling serial machines with flexible components and their embedded controllers. The optimization problem is treated using the direct design strategy which considers simultaneously structural and control parameters as variables and adopts non-convex optimization algorithms. Linear time-invariant and gain-scheduling PID controllers are addressed. This methodology is exploited for the multi-objective optimization of a pick-and-place assembly robot with a gripper carried by a variable-length flexible beam. The resulting design tradeoffs between system accuracy and control efforts demonstrate the advantage of an integrated design approach for mechatronic systems with configuration-dependent dynamics.     

Two-degree-of-freedom control with robust feedback control for harddisk servo systems

A two-degree-of freedom (2 DOF) control structure is proposed for read/write head servo systems of hard disk drives (HDDs). This structure is applied to both track seeking and track following, and makes mode switches found in conventional HDD servo systems unnecessary. Two innovative features introduced in the paper are: 1) a new method for generating the reference signal for track seeking and 2) two robust feedback control schemes for rejection of disturbances; one scheme uses a disturbance observer (DOB), and the other uses adaptive robust control (ARC). Simulation results show that the 2 DOF structure with ARC provides better performance than either the conventional servo system with mode switches or the 2 DOF structure with DOB. Experimental results show the advantage of the new reference generation method and the use of the DOB-based robust controller     

A new technique for robust control of servo systems

The robust controller has very simple structures and can be divided into two separate parts: a servo controller and an auxiliary controller. The two controllers are designed independently. The function of the auxiliary controller is to cancel out the plant uncertainties directly without the use of the high loop gain principle. Interpretation of robot controller as a signal-synthesis adaptive controller is given. Practical implementation issues of the auxiliary controller are discussed. Simulations of a design example with large parameter uncertainty, nonlinearity, and external disturbance are presented to demonstrate the effectiveness of the design technique. This technique is further tested with success in an experimental study of joint position control of a PUMA 560 robot arm     

Pole selection of feedforward compensators considering bounded control input of industrial mechatronic systems

A new pole selection method for feedforward compensators of mechatronic servo systems is presented in this paper. It is necessary to have the system poles located at desirable positions on the s-plane in order to realize better servoing performance. However, selection of new poles is not a straightforward problem and in most industrial mechatronic systems, it has been a mere cut-and-dry procedure. In this research, feedforward compensator poles are related to the control input, and a criterion was developed to determine the desirable poles that improve the control input within its limits. This method was developed for the second-order model and it was simulated and experiments were performed with the Performer MK3s articulated industrial robot manipulator. Some attractive results have been obtained with the new method.     

A design paradigm for mechatronic systems

Concepts of mechatronics are applicable in the design of complex and multi-domain dynamic systems. This paper presents an approach based on the mechatronic design quotient (MDQ) for systematic design of a mechatronic system. Traditional procedures of design are hierarchically separated into topological design and parametric design. Extending this concept, an MDQ may be “structured” into a multi-layered hierarchy. The approach and significance of the application of MDQ in mechatronic design are indicated using illustrative examples.     

A study on position servo control systems by frequency-lockedtechnique

A frequency-pumped controller (FPC) is presented that processes the position servomechanism by the frequency-locked technique. With the proposed FPC, a position/voltage (P/V) transducer, and a voltage-controlled oscillator (VCO), a frequency-locked position servo (FLPS) control system is established. Mathematical models for the FPC and for the FLPS are constructed, and their stability criteria for in-lock and for out-of-lock cases, respectively, are derived. Computer simulation and experimental results confirm the theoretical prediction that the proposed FLPS can provide real-time control, good stability, higher resolution, and higher precision     

Virtual prototyping of embedded control software in mechatronic systems: A case study

The large majority of technological devices can be seen as the sum of components of heterogeneous nature (electrical, mechanical, thermal, software, etc.) so that their analysis and design calls for the use of tools from different engineering disciplines. Integration among the different tools is particularly relevant at control system design level, since it is at this stage that it is required to analyze the behavior of both each single component and the system as a whole, with different levels of detail. In this paper mechatronic systems are considered, that exhibit a strong interplay between mechanical and electrical components, and the issue of modeling and designing embedded control algorithms and architectures for such systems is addressed. In particular, an integrated virtual prototyping approach for analyzing the system behavior down to embedded software level is proposed, that can be used in a wide number of situations that can represent the actual real-world operational conditions of consumer products. This approach can be used for system design (in particular at control systems level), embedded software design, and virtual testing so as to optimize and reduce the costs of late stage software development, physical prototypes, and their testing. The case study is based on some recently derived software tools that perform the co-simulation of the firmware execution and the multi-physical controlled system dynamics. The actual control software implemented in the final product can be entirely developed and tested inside the virtual prototype. To prove the validity and potentialities of the proposed approach, a real case study is presented, regarding a very common, though complex to simulate, mechatronic system such as an electric sliding gate. It turns out that the proposed environment goes beyond hardware-in-the-loop tools, since it does not require the use of specific hardware (the hardware itself is simulated in detail) but allows to analyze in detail the status of the microprocessors and peripherals at arbitrary time-scales and allows the designer to study at the earliest design stages the dynamics between the multi-physical controlled system and the firmware, without committing to a given hardware structure.     

Robust tracking control of mechatronic arms

A robust tracking control scheme based on variable structure systems (VSS) theory is presented to cope with the uncertainties and parameter variations in mechatronic arm dynamics. A modification of VSS is used to remove its restrictions with regard to chattering and required control efforts. By blending VSS with a self-organizing controller (SOC), a sliding mode self-organizing controller (SLIMSOC)scheme has been developed. In this scheme, both control actions and performance evaluation are executed using the distance from the desired sliding surface and rate of approach to it. Comparisons are drawn and it is shown that the inherent robustness properties of variable structure systems are retained while the undesirable chatter motion of the sliding mode is eliminated. The results are illustrated by applications of SLIMSOC on a direct drive SCARA type of robot.     

Integrated structure/control design of mechatronic systems using a recursive experimental optimization method

A recursive experimental design method for simultaneously optimizing both mechanical structure and control is presented in this paper. Control gains are optimally tuned for a given prototype of mechatronic system, and its mechanical structure is physically modified so that control performance can be further improved. The entire control tuning, evaluation, and structure alteration process is repeated until the desired performance goals are achieved. In each iteration, incremental design changes are determined based on a sensitivity Jacobian relating structural changes to performance improvements. The sensitivity Jacobian is updated during the recursive process using the actual data of the design changes. To estimate the Jacobian despite few data points, a pseudoinverse method and a parameter perturbation algorithm, termed singular-value excitation, are developed. The mechanical structure is modified recursively and quickly by using structure reinforcement and rapid prototyping techniques. The feasibility of mechanical structure changes is taken into account in determining the design changes. The proposed methodology is verified through simulation and applied to the design of a robot positioning system. The robot arm structure is modified with regard to stiffness and damping by using steel reinforced epoxy. PD control gains are optimized every time the structure is modified. Through the recursive procedure, an optimal combination of the arm structure and control gains is obtained.     

Modeling and design methodology for mechatronic systems

The integration of mechanical systems and microelectronics opens many new possibilities for process design and automatic functions. After discussing the mutual interrelations between the design of the mechanical system and digital electronic system the different ways of integration within mechatronic systems and the resulting properties are described. The information processing can be organized in multi levels, ranging from low level control through supervision to general process management. In connection with knowledge bases and inference mechanisms, intelligent control systems result. The design of control systems for mechanical systems is described, from modeling, identification to adaptive control for nonlinear systems. This is followed by solving supervision tasks with fault diagnosis. Then design tools for mechatronic systems are considered and examples of applications are given, like adaptive control of electromagnetic and pneumatic actuators, adaptive semiactive shock absorbers for vehicle suspension, and electronic drive-chain damping.     

On conceptual design of intelligent mechatronic systems

We have technology now to design networks of small intelligent units capable of competing and/or co-operating with each other on specified tasks and making decisions under conditions of uncertainty through a process of negotiation. In highly dynamic environments, such distributed systems are capable of achieving considerably better results in terms of performance/cost ratio and reliability than conventional centralised large systems and structures. The major elements of these systems are intelligent agents, which are software objects capable of communicating with each other, as well as reasoning about received messages. The paper discusses conceptual design of mechatronic systems based on multi-agent technology.     

An optimal variable structure control with integral compensationfor electrohydraulic position servo control systems

An approach using variable-structure control with integral compensation is presented for an electrohydraulic position servo control system to achieve accurate servo tracking in the presence of load disturbance and plant parameter variation. Simulations show that the proposed approach may give a rather accurate servo-tracking result and is fairly robust to plant parameter variation and load disturbance     

Modular design of mechatronic systems with function modeling

This paper develops a modularization scheme based on the functional model of a system. The modularization approach makes use of the function–behavior–state (FBS) model of the system to derive the entity relations. The design structure matrix (DSM) is automatically constructed based on the FBS model. In this way, the tedious work of filling the DSM entries based on expert knowledge is avoided. The approach makes use of k-means clustering algorithm to allow the user to try different number of clusters in a fast way. The k-means clustering is adopted for DSM based modularization by defining a proper entity representation, relation measure and objective function. Two modularization schemes are performed, one based on the immediate relations and one on the deeper behavioral relations between the components. Considering the application on the shifting system of the Delft University of Technology (DUT) Formula Student car, the latter modularization resulted in more mechatronic behavior based modules, while the former resulted in modules based on mere disciplinary and spatial closeness.     

Scaling-law-based metamodels for the sizing of mechatronic systems

This paper presents a new metamodel form and associated construction procedure adapted to the sizing tasks of mechatronics systems. This method of meta-modeling uses scaling laws to extract compact forms of design models from local numerical simulations (FEM). Compared to traditional metamodels (polynomial response surfaces, kriging, radial basis function) the scaling-law-based metamodels have the advantage of a light, compact form and good predictive accuracy over a wide range of the design variables (several orders of magnitude). The general regression process is first explained and then illustrated on different examples: a purely numerical test function, a limited angle electromagnetic actuator and a flexible mechanical hinge.