The Study On Static And Dynamic Characteristics And Lower Speed Stability Of Hybrid Differential Turntable

Rotary table is a machine accessory to realize the clamping work-piece, rotary and dividing positioning. Hydrostatic turntables are mostly used in the equipment manufacturing. There are some problems such as that lower speed movement is not smooth and lubrication oil heating is serious. This paper studys a new type of "differential" dynamic and static pressure turntable. This kind of turntable adds an independent high-speed rotation of central table between the upper table and the base. So even the upper table runs at lower speed, the turntable can keep larger speed difference between the upper table and the central table through the "differential" movement. This may eliminate the difference of static and dynamic friction at startup and guarantee the turntable lower speed stability. This research may open up a new way to improve the degree and positioning accuracy of large precise turntable. Based on the hybrid differential turntable as the research object, this paper analyzes the influence of geometric parameters and the oil cavity morphology on the static characteristics, as well as the influence of different conditions and the external load on the dynamic characteristics. This paper establishes the lower speed movement model and analysis its movement, finally uses the test-bed to do some related experiments.First, this article expounds the structure of hybrid differential turntable. And the Reynolds equation of logarithmic spiral groove is deduced based on the coordinate transform expression. The oil film thickness equation of spiral groove thrust bearing is listed. Based on flow continuity equation, the article analyzes the influence of the dynamic pressure oil cavity shape, number of groove, groove depth and static pressure oil cavity number on static characteristics. And this paper analyzes the relationship between static pressure oil cavity pressure and dynamic pressure inlet pressure, and the matching relationship between the bearing capacity of static pressure and dynamic pressure.Secondly, According to Newton’s law, the lower speed motion equations of turntable were established. By using the dynamic pressure equation, the process of system was calculated from initial state to a steady state. Then analysis the effect of static pressure oil supply pressure, the central table rotational speed, step load and periodic load on the system.Then, Transmission model of differential turntable is established and the equation of motion is listed. Through Matlab simulation this paper analyzes the lower speed stability and why the crawling phenomenon produces. Compared the turntable lower speed movement situation between pure hydrostatic lubrication and the hybrid differential lubrication, results show that the differential movement of central table could be a very good way to eliminate friction difference of dynamic and static pressure. The lower speed stability has a big enhancement.Finally, this paper introduces the structure of the test-bed, the layout of sensors, the hydraulic system, and turntable working principle and function. Design the scheme of turntable test. In accordance with the operating rules for experiments, collected and analyze the pressure, vortex, grating sensor signals under different working conditions. Results show that the hybrid differential table improves the lower speed precision.