Application Of Intelligent Speed Servo Control To Experimental Research On Optical Elastohydrodynamic Lubrication

Elastohydrodynamic lubrication (EHL) is the main lubricant style for those parts having point or line contacts. In this case, film thickness and shape are the major factors affecting the lubricating efficiency of machinery components. Influenced by some factors, the film shape and thickness in EHL for many machinery components are dynamic changed. In recent years, researches on elastohydrodynamic lubricated contacts under dynamic conditions have been focused. For most optical EHL test rigs, the current used servo control methods are so simple that the error between the reference and the actual motion is large to some extent. Therefore, the motion control system, as well as the control algorithm, is improved for the subsistent test rigs used under unsteady or spinning conditions. As a result, the measuring accuracy of film thickness and shape could be improved, and the following research on EHL problems under more rigor conditions could be carried on in future.The advancement of modern numerical control technique, fully support the development of high-accuracy EHL test rig in both hardware and software. Based on the review of EHL researches, many currently used EHL experimental methods are analyzed. According to the special accuracy of speed control in EHL experiment, a numerical controlled speed servo method is proposed, which is based on the intelligent motion control theory. Both multi-beam optical interference EHL test rigs without or with spin are redesigned using this new scheme, in order to reveal the real nature of EHL phenomena under unsteady or spinning conditions, and to perform the correlative experimental research on the film thickness and shape by changing speed, load and spinning-sliding ratio.In the film thickness measurement system, parameters of control and structure of the speed servo system are the main factors that affect the performance of the system, and are of time variation and uncertainty. As a result, a simple control method can not improve the dynamic performance of speed servo system. Integrated the advantages of self-adaptive control, fuzzy control and PID control, an intelligent dual module NC servo controller, called self-adaptive fuzzy PID (SAF-PID) controller is designed according to the modular design principle. Both fuzzy proportion and rule gene can be adjusted automatically by Matlab software under different working state. So the SAF-PID controller can change parameters and switch control methods automatically for the sake of adapting the system dynamic performances in the different work status.To validate the promoted SAF-PID controller, Matlab is used to simulate the speed servo control firstly. The step response and error response of SAF-PID controller can indicate the performance of rapid, steady and accuracy. Some disturbances are imported randomly to simulate the time variation and uncertainty of main parameters, such as control and load. So the interference killing features of speed servo control can be validated, such as the auto adjustment of control parameters, auto switch of control arithmetic, and the tracking precision of servo system. Then the proposed SAF-PID controller is used to control the start up process of EHL in pure sliding condition, in order to compare with the traditional results of experiment and numerical analysis, and to test this smart controller preliminarily.Experimental observation of EHL films under cyclic intermittent entrainment is carried out to validate the promoted SAF-PID controller, and three kinds of local film dimples have been identified. It is discovered that intermittent stops of the bounding surfaces generate clear lubricant entrapment and then film dimple due to squeeze effect, and pure rolling produced larger entrapment than that by pure sliding. Another local film dimple produced in the start-up process has also been demonstrated, which is attributed to the velocity perturbation. The peak velocity in the velocity oscillation results in an instantaneous larger lubricant entrainment and therefore local film dimple. The resultant crescent-shaped fringe moves through the Hertzian contact region at the entrainment speed. When pure disc sliding is employed, a cyclic inlet dimple appears due to boundary slippage effect. The results showed that the generation of the inlet dimple has strong dependence on the speeds and the time interval between two stops. Unlike those two dimples, the inlet dimple by the boundary slippage does not move through the contact region with the moving surface. In addition, the experiments displayed that the velocity perturbation effect from a sudden start-up was largely depressed under conditions of pure disc sliding. The observed phenomena can be explained by the squeeze effect, the entrainment effect and the wall slippage.Applied the SAF-PID intelligent speed servo control technology, the film thickness of a sliding EHL contact with spin has been measured by optical interference, and the effects of the spin on the film building up are studied. The main results are summarized as follows. It is demonstrated that in a ball-on-disc configuration spin motion can be superimposed on the conventional rolling/sliding EHL just by an offset of the contact center with respect to the disc rotation center, and the spin level is controlled by the offset. The EHL film shape is obviously skewed when spin motion is increased, and the symmetry of the conventional side lobes gets lost. Obvious film thickness reduction can be observed when spin level is high. The film thickness dependences on entrainment speeds are significantly influenced by the spin ratio Ssp. The film thickness at the low side lobe has the largest speed index. With decreasing spin motion, the speed indices of the two side lobes gets close. At high speeds, the film thickness difference of the two side lobes is large. In the present experiments, increasing loads can induce more effective spin effect within the EHL contact, and the difference between the two side lobe film thicknesses gets large and the horse-shoe film shape is more distorted. The spin raised by load decreases the overall film thickness.