This paper presents a high-efficiency compensation method of the dead zone with the aid of the adaptive dither for the ultrasonic motor. Prior to proposing the method, the influence of the dither on the principal elements of the dead zone, i.e., the deviations of the control variable and the minimum velocity, is analyzed. Then, the improved generation method of the adaptive dither is proposed, which introduces the adaptive dither by orthogonally adjusting the amplitudes of the applied voltages instead of changing the phase difference, as mentioned in the existing studies. Experimental measurements have demonstrated that the proposed method not only can effectively compensate the dead zone and conveniently control the velocity, but also is superior to the existing phase-difference-based method in terms of improving the efficiency of the ultrasonic motor.

Dead-Zone Compensation of an Ultrasonic Motor Using an Adaptive Dither

Implementation issues and testing of a hybrid sliding isolation system

Systems having dry friction nonlinearity can be stabilized by introducing intentional nonlinear passive compesation. For small ramp inputs it is necessary to increase the damping by a derivative control which becomes saturated for high ramp rates. To decrease the steady-state error at high ramp rates and achieve stability, a dead zone before the integrator is used. A scheme for an input adaptive system is also presented in this paper.

Nonlinear Compensation of a Second-and Third-Order System with Dry Friction

A historical development of mechanical and electronic differential analyzers as well as the significant developments in simulation techniques are discussed. Present-day application of modern analog and hybrid computers to electric power systems are presented. Included are the simulation of electric machines, static converter drives, transmission lines, and dc power systems. Special-purpose analog and hybrid computers are also discussed briefly. The material presented in this paper should enable an informed evaluation of the capabilities of analog and hybrid computers in the analysis of power system problems.

http://ieeexplore.ieee.org/iel5/5/31182/01451481.pdf

Applications of analog and hybrid computation in electric power system analysis

An investigation concerning the prediction and control of observed limit cycling behavior in a boosting rocket is considered. The suspected source of the nonlinear behavior is the presence of Coulomb friction in the nozzle pivot mechanism. A classical sinusoidal describing function analysis is used to accurately recreate and predict the observed oscillatory characteristic. From this analysis, insight is offered into the limit cycling mechanism and confidence is gained in the closed-loop system design. Nonlinear simulation is used to support and verify the results obtained from describing function theory. Insight into the limit cycling behavior is, in turn, used to adjust control system parameters to indirectly control the oscillatory tendencies. Tradeoffs with the guidance and control system stability/performance are also noted. Finally, active control of the limit cycling behavior, using a novel feedback algorithm to adjust the inherent nozzle sticking-unsticking characteristics, is considered. HE ballistic tactical target vehicle (BTT V) is a suborbital rocket whose re-entry vehicle serves as a target for advanced air defense and theater defense systems under development.1'2 Flight telemetry results from the first two missions indicate the presence of low-amplitude, low-frequency steady oscillations in both the vehicle attitude and actuator piston displacement.3'4 Figure 1 illustrates this characteristic in the vehicle pitch attitude response during second stage boost of the first mission. Note the flight data has been post processed. The impact of the oscillatory motions on the guidance and control objectives appear to have been minor; however, their presence was unexpected and is of concern, especially with regards concerning the origins of the oscillatory behavior and the physical mechanism by which they occur. The hardware in question is the decommissioned Minuteman I Stage 3 system which is used as the second stage for the BTTV vehicle. After discussions with individuals intimately familiar with the Minuteman I Stage 3 characteristics, it became known that this system has a long history of exhibiting small, slow periodic motions during the boost phase. These characteristics are, in fact, so common that routine preflight analysis is used in estimating the oscillatory motion for the specific flight vehicle/control system in question. The results are then compared with an existing database to deter- mine whether the oscillatory motions will impact the guidance and control mission objectives. This database suggests the oscillatory motions are limit cycling behavior due to nonlinearities present in the actuator-nozzle system, a conventional hydraulic actuator driv- ing vectorable nozzles. Coulomb or dry friction present in the nozzle pivot is the primary culprit. Additional nonlinearities are present but are not considered here. The first goal of this research is to provide an accurate prediction, if possible, of the oscillatory behavior experienced by the BTTV flight vehicle.5 This analysis should provide insight as to the ori- gin of and the mechanism by which the characteristics occur. Si- nusoidal describing function theory and nonlinear simulation are to be employed in achieving this goal. A second goal of this re- search is to explore means by which the oscillatory motions may be controlled to lessen the impact upon the guidance and control performance.5 The implemented control systems should also have minimal impact on the performance of the guidance and control feedback loops, while simultaneously providing sufficient robust- ness against reasonably expected modeling uncertainties and errors.

Dynamics and control of limit cycling motions in boosting rockets

The presence of coulomb friction in servomechanisms often results in undesirable effects, such as an operating dead-zone, low-frequency wander, and poor dynamic performance for low level signals. Methods of compensation for these adverse effects are discussed and a specific example is presented. Also, a general procedure, using frequency-response techniques, is outlined for the synthesis of compensation in systems affected by coulomb friction. The methods employed are based on the recognition that coulomb friction in a control device has a describing function which reduces gain and introduces phase lag. The describing function is determined by both the amplitude and the frequency of the input signal to the device.

Coulomb friction in feedback control systems

THE USE of dynamically faster drives in aircraft electric-power-generating systems precludes the assumption formerly made in computer studies of these systems that the electrical transient is much faster than the mechanical transient. Furthermore, the representation of alternators for parallel operation introduces new conceptual problems not formerly encountered in representing the alternator for isolated operation. In this paper, the basic circuit equations developed by Park are used to describe the alternator. An additional form is also used so that the effect of saturation is approximated. The usual procedure of breaking the system into its simplest units for system studies is followed in this presentation. The representations of the constraints imposed by the interconnection of the units are separated from the units themselves.

Vinton B. Haas

Papers

Coulomb friction in feedback control systems

Analog computer representation of alternators for parallel operations