Musa Jouaneh

Modeling hysteresis in piezoceramic actuators

Abstract A major deficiency of piezoceramic actuators is that their open-loop control accuracy is seriously limited by hysteresis. This paper discusses the adaptation of the Preisach model to describe the nonlinear hysteresis behavior of these actuators. The adapted model is used to predict the response of a piezoceramic actuator to a sinusoidal input and a triangular input. The predictions are compared with experimental measurements on a stacked piezoceramic actuator. The model reproduces the hysteresis loop of the actuator to within 3% over the entire working range of 0–15 μm. This opens the possibility of incorporating the model into a control loop in order to overcome the accuracy problem.

Generalized preisach model for hysteresis nonlinearity of piezoceramic actuators

This paper presents a new approach for modeling the hysteresis nonlinearity of a piezoceramic actuator using a modified generalized Preisach model, and the use of this model in a linearizing control scheme. The developed generalized Preisach model relaxes the congruency requirement on the hysteresis loops of a piezoceramic actuator, which must be satisfied when using the classical Preisach model. The congruency property is experimentally proved to not hold when running the actuator on a minor hysteresis loop. A numerical expression of the model is derived in terms of first- and second-order reversal curve experimental datasets. Output prediction using this model is performed on both an exponentially decayed sinusoidal input signal and an arbitrary input signal, and the results show that the model can accurately reproduce the hysteresis response with an error of less than 2.7%. A tracking control system for a piezoceramic actuator is also developed by combining a PID feedback controller with a hysteresis linearizing scheme in a feed-forward loop. The results show that this new control system can achieve 0.25 μm tracking control accuracy, which is 80 and 50% less than that obtained when using an open-loop controller and a regular feedback control system, respectively.

Design and characterization of a low-profile micropositioning stage

This paper discusses the design and characterization of a new, single-axis, low-profile, piezo-driven vertical motion micropositioning stage for use in laser welding applications. A low-profile configuration is attained by mounting the piezo actuator horizontally and using a novel lever arrangement to transfer the horizontal motion of the actuator into the desired vertical motion. An analytical model for the static and dynamic behavior of the stage is presented, along with finite element (FE) modeling verification. A 200 μm motion-range stage was built, and tests show that the stage has a vertical stiffness of 6.0 N/μm and a resonance frequency of 364 Hz. The results are in very close agreement to those predicted by the model.

Modeling of flexure-hinge type lever mechanisms

Abstract A general approach for the design of flexure-hinge type lever mechanisms that are commonly used in the design of translational micro-positioning stages is presented in this paper. The paper focuses on the development of design equations that can accurately predict the behavior of such stages especially the “lost motion” due to hinge stretching. The development of these equations is based on a static analysis of a general configuration of a single-axis, translational, flexure-hinge type, piezo-driven micro-positioning stage using a multi-lever structure. The displacement ratio between the input and output motions of one of the levers, plus the stiffness at either end of this lever are obtained based on the analysis. The overall displacement and stiffness of the micro-positioning stage are then obtained by cascading the individual results from every lever. The developed equations include the effects of the flexure hinge bending and stretching. The developed equations were applied to design of a vertical motion micro-positioning stage. The stiffness and displacement of this stage are predicated by these equations, which are compared to the stiffness and displacement directly obtained from the finite element modeling and actual testing of the same micro-positioning stage. The comparison shows that the analytical approach gave nearly similar results (within 10%), which implies that the developed equations can accurately predict the characteristics of flexure-hinge type lever mechanisms.

Trajectory planning for coordinated motion of a robot and a positioning table. I. Path specification

Coordinating the tool (robot) and workpiece (positioning table) motion in continuous manufacturing processes such as sealing, welding, and laser cutting offers several advantages over the motion of only the tool or workpiece. Better utilization of the speed and workspace characteristics of the two devices and improvement in tracking accuracy at sharp corners in the path are some of the merits of this approach. In coordinated motion, the two devices are simultaneously moved to track a given path, and two strategies are developed for coordinating their motion, where each is dependent on the given path information. The first strategy is applicable to any type of path and resolves the motion by splitting the displacement between any two points on the path into segments moved by the robot and the table. The robot and the table move in opposite directions in this strategy. The second strategy is applicable to sharp cornered paths and resolves the given path into two smooth paths. The first path is a double clothoid curve, whereas the second path is a tangential straight line path. The table executes a local motion around the corner in this strategy, whereas the robot is moved at all times. The uniqueness of this strategy in constructing the original corner path is proved. The proposed strategies are shown to be applicable to other coordinated motion systems. >

Trajectory planning for coordinated motion of a robot and a positioning table. II. Optimal trajectory specification

For pt.I see ibid., p.735-45 (1990). A robot and positioning table system is a kinematically redundant system with respect to planar motion. Two strategies were developed in pt.I to resolve this redundancy and to specify path shapes that make the best utilization of the workspace and speed characteristics of the two devices. In this part, a one-variable dynamic programming approach is developed to obtain a near-minimum time and/or energy trajectory of the two devices. The developed strategies were studied using this path-planning algorithm on a model of a 3 d.o.f. robot and a two-axis linear positioning table for a variety of path shapes and constraints. In addition, experiments were performed in a typical workcell to show the feasibility of the developed strategies. In moving the two devices in opposite directions, the least travel time is obtained when the original path is resolved more in favor of the faster device, whereas the quality of resultant motion is dependent on the controller performance of each device. >

Dynamic Modeling of a Two-Axis, Parallel, H-Frame-Type XY Positioning System

XY positioning is an important task in industrial applications. This paper addresses the dynamic modeling of a belt-driven, parallel-type XY positioning system constructed in the form of a capitalized H. The system uses one long timing belt to transmit the rotation of two stationary motors to end-effector motion. Due to less moved masses, the studied H-frame system is potentially capable of fast acceleration, and therefore, faster positioning than traditional stacked systems. The use of an elastic transmission element also causes the biggest disadvantage of the system, which is an uncertainty of end-effector position due to stretching in the belt. Thus, the objective of this paper is to develop a dynamic model that can capture the response of this system. Using Lagranges method, an eighth-order lumped parameter dynamic model of the stage motion is derived. The effect of nonlinear friction in the pulleys and cart motion is added to the model. The response of the model was simulated in MATLAB Simulink, and the model prediction is compared with real data obtained from the developed system. The results show that the model can accurately predict the dynamics of the developed H-frame positioning system.

A neural network model for invariant pattern recognition

A neural network is proposed to achieve invariant pattern recognition to binary inputs based on a computation of the invariance net and the ART1 neural network. Computer simulations show that the new network is plastic to unfamiliar inputs and requires no explicit training of the inputs. >

Backlash Compensation in Gear Trains by Means of Open-Loop Modification of the Input Trajectory

This paper presents an approach to reduce the effect of the backlash nonlinearity in systems with relative cyclic motion. A compensation approach is developed to calculate a modified course of input motion for a desired velocity profile in systems with known backlash. The modified input trajectory contains accelerating and decelerating motion features to traverse the backlash area in minimal time. The method was proved with a de-motor driven gear train. Results show that the output motion delay could be remarkably reduced. The time to overcome the backlash gap depends upon the desired velocity and the amount of backlash introduced to the system. Time savings between 43% and 74% could be measured with the utilized experimental setup. The proposed velocity compensation method is most efficient for low operating speeds and large mounting allowance between gears.

Measuring workpiece dimensions using a non-contact laser detector system

Proper process control procedures are important considerations in the optimisation of any manufacturing process. Ultimately, a continuous update on the size and quality of the products being manufactured is desirable. A non-contact laser detector system was developed to measure the dimensions of wood products in a real-time operating environment, employing a two-axis lateral effect photodiode as the sensor. Computer algorithms were developed to measure the thickness, warp, and width of wood samples (pencil slats). The effect of mechanical vibration due to slat transport was identified and when possible eliminated. The system was evaluated at different transport speeds. The results indicated that, except for width measurement which is limited by the computing speed, the system can measure thickness and warp quite accurately at feed speeds of 240 feet per minute. Although the work described is specific to certain applications, the implications for use in other industrial activities where visual sensing is required is apparent.