| Computer numerical control (CNC) machine tools are widely used in manufacturingindustry, which consume substantial amounts of energy and have a measurable impacton environment. Therefore, energy saving and emission reduction of machine tools isattracting more and more attention due to their environmental impact. However, manyenergy-consumption characteristic rules of CNC machine tool are still open becauseCNC machine tool usually has many energy consumption components which havecomplicated energy characteristics and cover multidiscipline fields including electrics,mechanics, and hydraulics. On the other hand, energy saving and emission reduction ofmachine tools is necessary for our national strategy because China remains the world’smost machine tools (about7million) but most of which have low energy efficiency. Forabove mentioned reasons, energy-consumption characteristic rules of CNC machine toolare investigated. The major contributions are as follows.CNC machine tool usually has many energy consumption components which havecomplicated energy characteristics and cover multidiscipline fields including electrics,mechanics, and hydraulics. Firstly, the entire machine-tool energy consumption can bedivided into two parts, i.e. load-independent consumption and load-independent energyconsumption. The former is quantificated by a series of switch-off functions andconstants, the latter is derived according to power balance equation, and consequentlyan integrated energy consumption model is proposed. The proposed model includes notonly the operational state of machine tools but also the real time load, transfersqualitative description of energy consumption to its quantification, and lays afoundation to monitor in real time the energy consumption state of machine tools.The spindle system of CNC machine tools has a continuous variable speed by usingconverter technique, which is different from the spindle system of conventional machinetools that has several step speed changes by using mechanical transmission. Therefore,the energy characteristics of spindle system of CNC machine tool are distinct from thatof conventional machine tool. The tare power of spindle system of conventionalmachine tool can be well approximated by a quadratic function in term of speed.Different from it, the tare power of CNC machine tool is a compound function in termsof speed, friction, and damping. Although the tare power function usually has minimumwhen the speed is above the base speed, it is difficult to determine due to the complex increasing and decreasing of the tare power function. For this reason, a sufficientcondition is given to judge quickly whether the tare power function has minimum whenthe speed is above the base speed.It is another problem for CNC machine tool spindle that the additional load loss isunable to be measured effectively. Taking the electric motor and mechanic transmissionas a whole, it is proven in theory that the additional load loss is a quadratic function interm of cutting power. Based on this conclusion, a practical method is proposed forengineering application that the additional load loss function can be fitted by a quadraticpolynomial technology with few experimental data.The energy characteristic of CNC machine tool feed system is complex because ithas many energy components and the feed motor, one of energy components, usuallyruns at very low speed. An energy model of feed system is proposed based on theenergy characteristic of each energy component. The energy model is function in termsof speed, load, friction, damping and other parameters. Then, the impacts of speed, load,friction, damping and pitch on the energy consumption are investigated, respectively.Based on the entire energy consumption model and energy characteristic of spindlesystem and feed system, an on-line approach for monitoring energy consumption isproposed, which doesn’t install torque sensor or dynamometer and provides the theoryand experimental data support for taking further energy-saving measures. |
PDF Full Text Request