On the Stability of Digital Position Control with Viscous Damping and Coulomb Friction

In this paper, we investigate the combined effect of viscous damping and Coulomb friction on sampled-data mechanical systems. In these systems, instability can occur due the sampling of the applied discrete-time controller which is compensated by the two different physical dissipation effects. In order to investigate the interplay between these, we focus on how the stable domain of operation is extended by the dry friction compared to viscous damping. We also show that dry friction causes concave envelope vibrations in this extended region. The analytical results, presented in the form of stability charts, are verified by a detailed set of simulations at different representative control parameter values

Friction Effects on Stability of a Digitally Controlled Pendulum

This paper investigates the stability of a digitally controlled pendulum with Coulomb friction as primary source of dissipation. We focus on the stabilizing effect of friction against vibrations due to the otherwise unstable parameter settings, and we show how the stable domain of operation is expanded compared to the undamped case. Continuous time and discrete switched models are simulated to get information about the stabilization effect of friction. A special concave vibration envelope is identified, validated by experiments and shown as a characteristic form of vibrations for digitally controlled systems with dry friction

Limitations Caused by Sampling and Quantization in Position Control of a Single Axis Robot

This paper presents the theoretical and experimental investigation of the dynamics of a single degree-of-freedom robotic arm subjected to digital position control. The experimental setup consists of an industrial robot axis, a microcontroller based low-level control unit, and a highlevel Matlab/Simulink position controller. The stable domain of operation is calculated in the parameter space of the sampling time and the gains of the applied proportional-derivative (PD) controller. The calculated stability charts are verified by experiments, and the paper reports the limitations on system stability caused by the digital effects and the applied control setup

Effect of immersion fluid temperature on the chicken embryo in teratogenicity tests: Short communication

The influence of immersion fluid temperature on the development of the chicken embryo was studied on the day most commonly used for treating incubated eggs in teratological trials. Embryonated eggs were immersed in tap water for 30 min on the 12th day of incubation at 22–25 °C or at incubation temperature without a waiting time or after 30 min. The incubation was then continued and the eggs were processed on day 19 of the incubation period. Treatment of eggs at 22–25 °C caused a significant increase in embryonic mortality, while the 30-min waiting time did not exert an influence on embryogenesis