Rudolf J. Seethaler

An upper-bound cutting model for oblique cutting tools with a nose radius

The geometry of practical cutting tools is complex, and usually involves both non straight cutting edges and obliquity. It is of great practical importance to be able to predict cutting forces and chip flow directions for such tools. The authors demonstrate the use of a simplified geometry together with an upper bound model to predict the direction of chip flow. The model proposed includes a requirement for approximate force equilibrium as a method of estimating rake face contact area. A comparison of the results with those from earlier models and with experimental data is provided. Finally a proof of the Stabler chip flow hypothesis is given: it is shown that the hypothesis is only valid for the case of zero rake face friction.

Sensorless Position Control For Piezoelectric Actuators Using A Hybrid Position Observer

Soft piezoelectric actuators are extensively used in micro- and nanopositioning applications. Traditional sensorless position control approaches use a hysteresis mapping between voltage and position in a voltage feedforward control scheme in order to compensate for hysteresis errors. However, several factors such as frequency, temperature, and aging influence this mapping. Recently, charge control for positioning is also attracting interest among researchers due to the linear relationship between position and charge. However, a sophisticated hardware design is required to minimize charge drift. In this study, a new sensorless position control technique is proposed which requires neither an accurate inverse mapping nor a sophisticated charge amplifier in order to compensate for hysteresis. A constitutive relationship is employed to infer position from charge measurement through current integration. To eliminate drift from the charge-based measurement, an observer is presented in this study which uses a second self-sensing position estimate that is based on the variation of effective piezoelectric capacitance with stroke. The proposed observer is tested as a position feedback sensor inside a simple integrating control loop and applied to step profiles of variable stroke and sinusoidal profiles of constant and mixed frequencies. The responses are compared with a laser interferometer and the maximum observer error between the laser and the observer is 0.89 μm ( 3% of the maximum stroke) over a frequency range of 10 to 100 Hz.

A Fully Flexible Valve Actuation System for Internal Combustion Engines

The automotive industry has been under continued pressure to improve fuel efficiency because of air pollution, global warming, and rising gasoline prices. One technology to address this need is electronic valve timing. It promises to achieve fuel savings of 10%-15% by reducing pumping losses, introducing cylinder deactivation, and enabling new combustion strategies, like homogeneous charge compression ignition. To date, valve actuators for this application primarily rely on resonant spring arrangements to achieve the necessary dynamics. This leads to a fixed amplitude of the valve trajectory and only allows for variable valve timing. In this paper, a fully flexible valve actuation system for intake valves is introduced that provides variable lift in addition to variable timing, without reducing valve dynamics or energy efficiency. Optimization procedures for the mechanical system, the servo motor selection, and the valve trajectory are presented. The combined effect of these optimizations leads to valve accelerations that are an order of magnitude higher than conventional electric servo systems. Simulations and an experimental test bed are used to validate the system performance. A comparison with other electronic valve actuation systems confirms the excellent performance of this approach.

The Identification of Radial Runout in Milling Operations

The authors discuss a novel approach to estimation of individual tooth runout in milling. The approach is based upon a simplified linear force model and leads to good results at high values of immersion. Two variants of the approach for estimating runout are presented. The first method utilizes torque while the second considers in plane force components as indicators of runout. Simulations are used to verify the equations that were derived for relating runout to in plane forces and to allow the assessment of the influence of the spacing of the discrete force samples on accuracy. Experimental evidence validates the approach for a wide range of immersion values. Experiments also show that the approach is able to identify edge breakage in the presence of significant initial runout.

Process control and dynamic process planning

Real time machine tool control and the planning activities which precede manufacture are usually interfaced through a low level language which allows little more than position, feed, and speed information to be passed between the two systems. The higher level systems used to describe geometry and tool paths also lack an adequate capability to describe manufacturing processes. The authors discuss the provision of a much richer interface between the planning and control activities which both facilitates the identification and scheduling of suitable monitoring tasks and allows the updating of process plan data from real time measurements. The result of such integration is an improvement in the efficiency of real time optimisation, and perhaps most importantly the possibility of quasi real time process planning. A system that is able to perform both initial process planning and plan refinement based upon low level feedback must also encompass the path generation activity, such a system is referred to by the authors as a dynamic process planning system. The paper describes the fundamentals of the process models, identification algorithms, control strategies, and low level process plan generation used within such an integrated system.

The regulation of position error in contouring systems

Abstract The authors discuss the use of a novel hardware configuration in the control of position error during contouring operations. The architecture described allows real time error control in multiple axis systems; this is achieved by allowing any axis with a phase lag which exceeds that specified, to slow down the entire system until it is in conformance. The performance of the system is demonstrated by both simulation and experiment, using cornering and circular interpolation as examples. The major contribution of the work is thought to be the ability of the system to cope, in real time, with system constraints and nonlinearities.

Novel Method for Interstory Drift Measurement of Building Frames Using Laser-Displacement Sensors

AbstractInterstory drift measurement is a critical parameter for determining earthquake damages in civil engineering structures. It can be measured using global positioning systems (GPS), accelerometers, LVDTs, and so forth. Each of these methods has limitations in terms of accuracy, cost, installation, and so on. In this study, a novel, laser-based in situ interstory drift measurement setup is proposed and tested on a shake table on which the laser sensors were mounted in the frame to measure interstory drift without any reference frame. The in situ measurements are compared with measurements from reference lasers, which are mounted on a frame separate from the structure.

Experimental Validation of a Cogging-Torque-Assisted Valve Actuation System for Internal Combustion Engines

Electromechanical valve actuation (EVA) is an emerging technology that aims to optimize valve trains, allowing for significant improvements to engine performance, efficiency, and emissions. Recently, a simulation study introduced a novel cogging-torque-assisted motor-driven (CTAMD) valve actuation system. The actuator design emphasized a large output cogging torque that removed the need for conventional valve springs. The cogging torque developed by this actuator allows for highly efficient energy recovery that is superior to comparable systems that make use of mechanical springs. This paper experimentally validates the simulation study with a prototype actuator constructed using the specifications suggested in the previous simulation. The characterization procedure of the prototype is discussed and close agreement is found between the simulated and experimental motor parameters. Furthermore, this paper details a control system that minimizes Ohmic loss while providing fast transition times and low seating velocities. Finally, experimental results are displayed and compared to the simulated results as well as other EVA systems to validate the conjectured speed and efficiency of the CTAMD system.

Hysteresis independent on-line capacitance measurement for piezoelectric stack actuators

Piezoelectric actuators are typically modeled as capacitive elements for control purposes. An important model parameter, clamped capacitance, is traditionally considered constant and obtained through offline measurements. However, the capacitance value changes with operating conditions such as electric fields, environmental temperatures, and aging. In addition, traditional capacitance measurements are not hysteresis free. In this research, a hysteresis independent real time capacitance measurement technique is proposed. This is achieved by superimposing a high frequency ripple over the normal control voltage signal and comparing the resulting current signal to the voltage ripple. Since the mechanical bandwidth of the actuator is much lower than the ripple voltage, no measurable movement is induced by the measurement technique, and a clamped capacitance is determined. It is demonstrated that the measurement is largely independent of hysteresis and it shows good agreement with an LCR meter. The on-line capacitance measurement is very useful for characterising piezoelectric actuators and for implementing more robust control schemes.

On the feasibility of using measurements of charge and effective capacitance for simultaneous position and force self-sensing of piezoelectric actuators

In this study a new relationship between effective capacitance, position, and force of a piezoelectric actuator is presented. This relationship in combination with an existing constitutive relationship between charge, position, and force, can pave the way for simultaneous sensorless position and force identification. A test setup is built to study the feasibility of using the proposed relationship. Satisfying experimental correlation between effective capacitance, force, and position has been achieved using a second order Taylor series.