Combined electric drive with automatic transmission gears for CNC machines

Abstract

One of the main modes on turning machines is the processing mode with constant cutting speed and feed per the spindle revolution. The main motion drive in this case operates in constant power mode. There are three main options for spindle speed control: stepless, stepped and combined. For heavy turning machines, the last two options are the most acceptable, since they allow rational use of the engine in terms of torque and power when processing large-sized products. However, switching the stages of an automatic transmission leads to shock loads and deviations from the specified technological processing modes. The article considers the problem of minimizing the impact of shock loads on the cutting process through coordinated control of the electric drive and automatic transmission. Based on the Heaviside step function, a representation of the automatic transmission clutch as a link characterizing the discrete nature of power transmission is given. A mathematical description of the model of the spindle drive power circuit as a three-mass structure is given, in which the processes of switching automatic transmission stages are represented by keys and parametric links. When describing the belt drive, the tension of the belt in the form of a nonlinear link is taken into account, which determines the areas of static and sliding friction. The identified conditions for shockless switching made it possible to develop a control structure for an adjustable electric drive with a proactive change in speed relative to the moments of switching gear stages. Studies of transient processes using a simulation model of face machining for a CNC machine have shown that the impact of switching gear stages on the machining process can be minimized. The developed model of the main drive power circuit made it possible to summarize the basic properties of the automatic transmission and belt drive. The basic requirements for control tasks of a combined electric drive for distributed CNC structures are formulated, in which the NC system core and Soft PLC are connected via a protocol based on the Ethernet network.