Method for determining a critical point in time for energy saving for the standstill of the spindle of an NC machine tool and for energy saving
Patent Information
- Application Number
- DE112020003251
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- Priority Date
- 2020-10-21
- Filing Date
- 2020-11-06
- Publication Date
- 2025-10-26
- Estimated Expiration
- 2040-11-06
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
Technical area
[0001] The present invention relates to the field of energy saving by stopping a spindle of an NC machine tool, in particular methods for determining a critical time for energy saving for the standstill of the spindle of an NC machine tool and for energy saving. Background technology
[0002] As a major manufacturing nation, China leads the world in the possession of NC machine tools, and its energy consumption is enormous. Non-value-adding activities in the machining process of NC machine tools account for a relatively large portion of this energy waste. Therefore, it is crucial to investigate energy consumption and energy-saving technologies in the machining process of NC machine tools.
[0003] Current research on reducing energy consumption in the operation of machine tools generally uses methods to achieve high energy efficiency, including the conversion of NC machine tools, process scheduling optimization of the machining process, optimization of the process parameters of NC machine tools, energy-saving control of machine tools, etc. Energy-saving control of machine tools is crucial because the energy consumption of the spindle system of NC machine tools represents a relatively large proportion of the total energy consumption. However, a complete and effective method for idling the spindle system of NC machine tools to save energy is currently lacking.
[0004] NC machine tools and methods for their optimization are known, for example, from the following publications: 1) Huajun CAO, Yi LUO. Analysis and development prospects of high-efficiency green machine tool technology[J]. Metal Processing (Cold Working), 2012, (12) pages: 14-17 2) Ji Q, Li C, Zhu D, et al. Structural design optimization of moving component in CNC machine tool for energy saving[J]. Journal of Cleaner Production, 2020, 246: 118976. 3) Lin KONG, Liming WANG, Fangyi LI, et al. Green production scheduling of hybrid flow shop based on machine tool matching characteristics[J]. Computer Integrated Manufacturing Systems, 2019, 25(05): 1075-1085. 4) Congbo LI, Song FU, Zhengzheng CHEN, et al. Multi-objective optimization model of CNC gear hobbing processing parameters for high efficiency and energy saving[J]. Computer Integrated Manufacturing Systems, 2020, 26(03): 676-687. 5) Zhang C, Jiang P. RFID-driven energy-efficient control approach of CNC machine tools using deep belief networks[J]. IEEE Transactions on Automation Science and Engineering, 2019, 17(1): 129-141. Content of the invention
[0005] The present invention aims to provide a method for determining a critical point in time for energy saving by spindle standstill based on the target spindle speed before cutting, and for achieving standstill for energy saving in an NC machine tool spindle system based on the time between the critical point and the two cutting activities, as well as predicting the energy saving effect based on the relevant parameters. This and other problems are solved by an energy saving method with the features of claim 1.
[0006] The method for determining a critical point in time for energy saving during spindle standstill of an NC machine tool, as well as for energy saving, comprises the following steps: Step 1: The motion process of the NC machine tool spindle system is divided into two parts: a stationary process and a transient process. The total energy consumption E of the motion process of the NC machine tool spindle system is calculated as: E=ES+ET where E denotes the total energy consumption of the motion process of the NC machine tool spindle system; where E S the energy consumption of the steady-state process at spindle speed n; where E T the energy consumption of the transient process of spindle acceleration from the initial speed n0 to the target speed n1. Step 2, the energy consumption of the NC machine tool spindle system for the stationary process comprises two components, namely the energy consumption for spindle rotation P SR (n) and the energy consumption for the basic machine tool module P B , which can be calculated as follows: ES=PSt=[PSR(n)+PB]t where P S The steady-state process power at spindle speed n is denoted; P SR (n) the spindle rotational power at spindle speed n; P B the power output of the basic module of the machine tool; t the steady-state process duration. Step 3, the energy consumption of the transient process of the NC machine tool spindle system can be calculated as follows: ET=∫0tT1PT1 dt+PB(tT1+tT2)+12[PSR(n0+30αtT1π)+Ts(πn030+αtT1)+PSR(n1)]tT2 where t T1 denotes the time of the spindle rotation acceleration process, s; P T1 The power of the spindle rotational acceleration, W; PB the power of the NC machine base module, W; t T2 the time of the spindle turning transition process, s; P SR () the power function of the spindle rotation; n0 the initial spindle speed, rpm; α the angular acceleration of the spindle rotation acceleration process, rad / s 2 ; T S the acceleration torque of the spindle rotational acceleration, N·m; n1 the target speed of the spindle rotational acceleration, r / min. Step 4, NC machine tool spindle to standstill for energy saving should meet the following conditions: (1) The time between machining activities should be greater than the critical time for spindle standstill to save energy. (2) The energy consumption during the restart and acceleration process to the target speed after the spindle has stopped should be less than the energy consumption during the constant rotation of the spindle at the original speed (the original speed being equal to the target speed).
[0007] The equation is given as follows: where t I denotes the time between two machining operations, s; t min the critical point for spindle standstill to save energy, s; P SR () the power function of the spindle rotation; n1 the target speed of the spindle, rpm; P B the power output of the machine base module, W; t T the transient process time of the spindle rotational acceleration, s; E T the transient process energy consumption of the spindle system, J. Step 5, the critical point in time for spindle standstill to save energy in the NC machine tool system, should meet the following conditions: (1) The critical time for stopping the spindle to save energy should be greater than or equal to the time for the transient process acceleration of the spindle rotation; (2) Within the same time period (this is the critical time point), the energy consumption during the process of the spindle being stopped for a period of time and restarting and accelerating to the target speed is equal to the energy consumption during which the spindle continues to run at the original speed (the original speed is equal to the target speed).
[0008] The equation is given as follows: { tmin≥tTtmin(PSR(n1)+PB)=(tmin−tT)PB+ET where t min denotes the critical point in time when the spindle stops to save energy, s; tT the time of the transient process for accelerating the spindle rotation, s; P SR () the power function of the spindle rotation; P B the power of the basic module of the machine tool, W; E T the energy consumption of the transient process of the spindle system, J. Step 6, the critical point in time for energy saving through standstill of the spindle of the NC machine tool, can be calculated as follows: tmin=12tT12(ASR30αtπ+Tsα)+tT1BSR+12tT2[ASR(30αtT1π+n1)+TsαtT1+2BSR]ASRn1+BSR where t T1 denotes the time of the spindle rotation acceleration process, s; A SR the coefficient of the primary term of the formula for spindle rotation power; α the angular acceleration of the spindle rotation acceleration process, rad / s 2 ; T S the acceleration torque of the spindle rotation acceleration, N·m; B SRthe constant term of the formula for spindle rotation power; t T2 the time of the spindle rotation transition process, s; n1 the target speed of the spindle, r / min. Step 7, the energy saving achieved through the energy-saving method of the NC machine tool's spindle system by stopping the rotation, can be calculated as follows: ESA=tI(PSR(n1)+PB)−(tI−tT)PB−ET where E SA denoted as energy saved by the energy-saving procedure with standstill, W; T I the time between two machining operations, s; P SR () the power function of the spindle rotation; n1 the target speed for the spindle, rpm; P B the power of the basic module of the machine tool, W; t T the time for the transient acceleration of the spindle rotation, s; E T the energy consumption of the transient spindle system, J.
[0009] It can still be represented as follows: ESA=(tI−tmin)PSR(n1) where t I denotes the time between two machining operations, s; t min the critical point for spindle standstill to save energy, s; P SR () the power function of the spindle rotation; n1 the target speed for the spindle, rpm.
[0010] In step 3, the angular acceleration α and the acceleration torque T can be determined. S during the acceleration of the spindle rotation by an experiment to start the spindle and t T2 This can be determined by experimentally collecting and analyzing data.
[0011] In step 3 t T1 as follows: tT1=2π(n1−n0)60α where n1 denotes a target speed of the spindle rotational acceleration, r / min; n0 an initial speed of the spindle rotational acceleration, r / min; and α an angular acceleration of the spindle rotational acceleration process, rad / s 2 .
[0012] Compared to the previous state of the art, the present invention has the following advantageous effects: The method of the present invention obtains the energy consumption model of the transient and steady-state conditions of the spindle system of the NC machine tool by collecting and processing some basic data of the NC machine tool and then further processing it. A condition model and a model of the critical time for standstill and energy saving of the NC machine tool spindle system are then created, and the critical time for standstill and energy saving is calculated. Subsequently, the energy saved by standstill is calculated to determine how to save energy by properly stopping the NC machine tool spindle.
[0013] The method of the present invention is relatively easy to use, and the critical point for energy saving through spindle standstill in an NC machine tool is precisely calculated, and the prediction of energy savings is highly accurate. This allows for precise calculation and control of energy savings during spindle standstill in NC machine tools, providing a more accurate method for energy-saving control of NC machine tools. The method of the invention is practical and easy to implement; it can provide theoretical and technical support for energy-saving and emission-reduction strategies in the machine tool industry and even nationwide. Attached drawings Fig. Figure 1 shows a schematic representation of the process of the present invention. Fig. Figure 2 shows a schematic representation of the basic parameters of the method of the present invention. Fig. Figure 3 shows a schematic representation of the energy consumption in the method of the present invention. Specific ways to implement
[0014] The present invention is described in more detail in connection with the statements and the attached drawings.
[0015] The present invention presents a method for determining a critical point in time for energy saving during spindle standstill of an NC machine tool, as well as for energy saving in general. As described in Fig. As shown in Figure 1, this method consists of dividing the machining process of the NC machine tool spindle system into two parts: a stationary process and a transient process. Energy consumption models for the stationary and transient processes of the NC machine tool are then created. Subsequently, the condition model and the critical time model for energy savings during spindle standstill are established, and the critical time is calculated. Finally, the energy-saving model for energy savings during spindle standstill is created using the relevant data.
[0016] This embodiment of the invention uses the CK6153i NC machine tool as an example. Since the main drive system of the CK6153i NC machine tool contains four gears, the speed is categorized as AH, BH, AL, and BL from high to low. Because the AH gear has the largest machining range and is used most frequently, it is used for calculation and illustration in this embodiment. This method is used to obtain the power and energy consumption values of its spindle system in the AH gearbox and to implement energy-saving control during standstill. 1. Performance measurement of the NC machine tool basic module
[0017] The performance of the basic module of the NC machine tools P BThe power output of the basic module of several NC machine tools is determined by collecting the average value. After starting the CK6153i NC machine tool, no operation is performed on the machine, and the NC machine tool is left in standby mode. In this state, 100 sets of power values for the NC machine tool's basic module are measured. Then, the power output of the NC machine tool's basic module is calculated using the formula: PB=∑i=1NPB_iN, The final calculation of the performance of the NC machine tool basic module CK6153i is: PB=∑i=1100PB_i100=332,1W. 2. Power measurement in stationary processes for spindle systems of NC machine tools
[0018] The CK6153i NC machine tool is in standby mode, and the spindle is controlled to rotate at 500 rpm for a period of time to allow the machine tool to warm up sufficiently. The spindle is then controlled to rotate at various speeds to maintain a stable spindle speed.
[0019] After processing the collected data, the following performance model of the spindle rotation is obtained: PSR(n)=1.09n+41.12 (0 rpm) <n≤1000r / min) where P SR (n) denotes the power of the spindle rotation at speed n, W; n denotes the spindle speed, rpm.
[0020] The stationary process power P S The performance of the NC machine tool spindle system can be derived from the performance of the NC machine tool basic module P. B and the power of the spindle rotation P SR (n) are calculated, which is calculated as follows: PS=1.09n+373.22 (0 rpm) <n≤1000r / min) where n denotes the spindle speed, rpm. 3. Recording the energy consumption in the stationary process of the spindle of the NC machine tool
[0021] The energy consumption in the stationary process of the spindle of the NC machine tool can be calculated from the power of the spindle rotation, the power of the machine tool's basic module and the duration of the stationary process, and the calculation formula can be calculated as follows: ES=[PSR(n)+332,1]t where P SR () denotes the function of the spindle power; n the spindle speed, rpm; t the steady-state process duration of the spindle of the NC machine tool, see. 4. Recording the energy consumption during the transient process of the spindle of the NC machine tool
[0022] The experiment to start the spindle yields the angular acceleration α = 39.78 rad / s and the torque of the spindle acceleration T. S = 28.42 N·m of the AH drive chain of the NC machine tool. By substituting α and T S into the equation for spindle rotational acceleration P T1 This results in the equation for the spindle rotational acceleration P. T1 as follows. PT1=PSR(n0+380t)+2.98n0+1130.7t (0 <t≤tT1) where P SR () denotes the power function of the spindle rotation; n0 the initial spindle speed, rpm; t the time of spindle rotation acceleration, s.
[0023] The equation for the process time of the spindle rotational acceleration t T1 is calculated as follows: tT1=0.002632(n1−n0) where n0 denotes the initial spindle speed, r / min; n1 denotes the target spindle speed, r / min.
[0024] The transition time of the spindle t T2The change from peak power to stable power is related to the target spindle speed n1. The process time t T2 , corresponding to the different target speeds n1, is collected, and the process time t T2 The equation is regressed linearly against the target velocity n1. The equation is calculated as follows: tT2=0.0037+1.471×10−4n1 (R2=0.9479)
[0025] The equation for the transient process time t T The spindle system is calculated as follows: tT=2.7791×10−3n1−0.002632n0+0.037 where n0 denotes the initial spindle speed, r / min; n1 denotes the target spindle speed, r / min.
[0026] The energy consumption of the transient process of the NC machine tool can be calculated from the energy consumption of the spindle rotation acceleration process, the energy consumption of the spindle rotation transition process, and the energy consumption of the machine tool's base module during the transient process. The equation is calculated as follows: ET=∫00.002632(n1−n0)PSR(n0+380t)+2.98n0+1130.7t dt++12[PSR(2.00016n1−0.00016n0)+2.9760024n1+3.9976×10−3n0]××(0.037+1.471×10−4n1)+332.1×(2.7791×10−3n1−0.002632n0+0.037) where P SR () denotes the function of the spindle power; n0 the initial spindle speed, rpm; n1 the target spindle speed, rpm. 5. The conditions to be met for the energy-saving standstill of the spindle of an NC machine tool
[0027] In order to achieve energy savings through the standstill of the spindle system, the following two conditions must be met: (1) The time between two machining activities should be greater than the critical time for spindle standstill in order to save energy. Since the critical time is the minimum time required to achieve energy savings through standstill, the energy-saving effect cannot be achieved if the time between two machining activities is less than the critical time, as in Fig. 2 shown. (2) The energy consumption during the restart and acceleration process to the target speed after the spindle has stopped should be lower than the energy consumption of the spindle maintaining its initial speed (the initial speed being the same as the target speed). Essentially, the energy consumption of the spindle rotation at the target speed (such as the sum of the energy consumption in ranges 2, 3, 4, 5, 6 in) is Fig. 3) greater than the sum of the energy consumption during the acceleration of the spindle rotation process and the energy consumption during the spindle rotation transition (such as the sum of the energy consumption in areas 1, 4, 5, 6 in Fig. 3).
[0028] The equation is calculated as follows: {tI>tmintIPSR(n1)>ET1+ET2 where t I denotes the time between two machining operations, s; t min the critical point for spindle standstill to save energy, s; P SR () the power function of the spindle rotation; n1 the target speed of the spindle, rpm; E T1 the energy consumption for the acceleration process of spindle rotation, J; E T2 the energy consumption for the transition of the spindle rotation, J. 6. The conditions to be met for the critical point in time for energy-saving standstill of the spindle systems of an NC machine tool.
[0029] The critical point in time for the standstill of the spindle system of an NC machine tool to save energy should meet the following two conditions: (1) The critical standstill time of the spindle for energy saving should be greater than or equal to the transient process time of the spindle rotational acceleration. If the critical time is less than the transient process time of the spindle rotational acceleration, the spindle cannot complete the acceleration activity within a limited time after standstill so that the spindle speed reaches the target speed, as described in Fig. 2 shown. (2) Within the same time period (this is the critical time point), the energy consumption during the process of the spindle being stationary for a period of time and restarting and accelerating to the target speed is equal to the energy consumption of maintaining the spindle rotation at the initial speed the entire time (the initial speed being equal to the target speed). In essence, the energy consumption of the spindle at the target speed at the time the critical time point is reached (e.g., the sum of energy consumption ranges 3, 4, and 6 in [reference]) is [reference]. Fig. 3) equal to the energy consumption of the acceleration process of the spindle rotation and the sum of the energy consumption of the transition process of the spindle rotation (e.g. the sum of energy consumption areas 1, 4 and 6 in Fig. 3). {tmin≥tTtminPSR(n1)=ET1+ET2 where t mindenotes the critical point in time when the spindle stops to save energy, s; t T the duration of the transient process of the spindle system, s; P SR () the power function of the spindle rotation; n1 the target speed of the spindle, rpm; E T1 the energy consumption for the acceleration process of spindle rotation, J; E T2 the energy consumption for the transition of the spindle rotation, J. 7. Calculating the critical time
[0030] The critical time t min is calculated as follows: {tmin≥2.7791×10−3n1+0.037tmin=3.4637×10−6n12(380ASR+1130.7)+0.002 632n1BSR++(0.0185+7.37×10−5n1)(2.00016n1ASR+2.98n1+2BSR)ASRn1+BSR where t min the critical point in time for energy saving through standstill of the spindle system of NC machine tools, s; A SR the coefficient of the primary term of the formula for spindle rotational power; B SRthe constant term of the formula for spindle rotational power; n1 the target velocity of the spindle acceleration, see. 8. Predicting the energy-saving effect of energy savings through standstill of the spindle system of NC machine tools
[0031] Energy savings are achieved by using the method of standstilling the spindle system of NC machine tools to conserve energy. The energy savings can be calculated as follows: ESA=(tI−tmin)(ASRn1+BSR) where t I denotes the time between two machining operations, s; t min the critical point in time for energy saving through standstill of the spindle system of NC machine tools, s; A SR the coefficient of the primary term of the formula for spindle rotational power; B SR the constant term of the formula for spindle rotational power; n1 the target velocity of the spindle acceleration, see.
[0032] For example, after the spindle system of the CK6153i NC machine tool has completed the last machining activity, 6.5 s remain until the next machining activity, and the target spindle speed n1 for the next machining activity is 900 rpm. Since the target spindle speed is within (0,1000), the coefficient of the primary term A is SR the formula for spindle rotational power 1.09 and the coefficient of the constant term B SR 41.12. Then the above information is incorporated into the solution equation for the critical time t. min used to obtain, {tmin≥tT=2,54tmin=4,73 Since the time between two machining activities of the spindle is 6.5s greater than the critical time of 4.73s, the spindle can stop rotating after the previous machining activity has finished and then start rotating 2.54s before the start of the next machining task, which, using the formula to predict the energy saving effect, can save 1809.15 J of energy.
[0033] This method of the invention can determine the critical point for energy savings through standstill of the spindle system of NC machine tools and predict the energy-saving effect. The calculation results can be used directly for energy-saving control of the spindle system of NC machine tools and provide theoretical and technical support for the energy-saving and emission reduction strategies of the machine manufacturing industry and even the country as a whole.
[0034] Finally, it should be noted that the above embodiments serve only to illustrate the technical solutions of this invention and are not intended to limit it. Modifications or equivalent substitutions of the technical solutions of this invention, without deviating from the purpose and scope of the method of this invention, fall within the scope of the claims of this invention.
Claims
[1] Method for determining a critical time for energy saving for the standstill of the spindle of an NC machine tool and for energy saving, characterized by that it includes the following steps: Step 1, the motion process of the NC machine tool spindle system is divided into two parts, namely a stationary process and a transient process, whereby the total energy consumption E of the motion process of the NC machine tool spindle system is calculated as: E=E S +E T where E denotes the total energy consumption of the motion process of the NC machine tool spindle system; E S the energy consumption of the steady-state process at spindle speed n; E T the energy consumption of the transient process of spindle acceleration from the initial speed n0 to the target speed n1; Step 2, the energy consumption of the NC machine tool spindle system for the stationary process comprises two components, namely the energy consumption for spindle rotation P SR (n) and the energy consumption for the basic machine tool module P B , which are calculated as follows: ES=PSt=[PSR(n)+PB]t E S =P S t=[P SR (n)+P B ]t where P S The steady-state process power at spindle speed n is denoted; P SR (n) the spindle rotational power at spindle speed n; P B the performance of the basic module of the machine tool; t the steady-state process duration; Step 3, the energy consumption of the transient process of the NC machine tool spindle system is calculated as follows: ET=∫0tT1PT1dt+PB(tT1+tT2)+12[PSR(n0+30αtT1π)+Ts(πn030+αtT1)+PSR(n1)]tT2 where t T1 denotes the time of the spindle rotation acceleration process, s; PT1 The power of the spindle rotational acceleration, W; P B the power of the NC machine base module, W; t T2 the time of the spindle turning transition process, s; PSR(n0+30αtT1π) the power of the spindle rotation at the spindle speed n0+30αtT1π, W; n0 the initial spindle speed, rpm; α the angular acceleration of the spindle rotational acceleration process, rad / s 2 ; T S the acceleration torque of the spindle rotational acceleration, N·m, n1 the target speed of the spindle rotational acceleration, r / min; Step 4, NC machine tool spindle to standstill for energy saving meets the following conditions: (1) The time between machining activities is greater than the critical time for spindle standstill for energy savings; (2) The energy consumption during the process of restarting and accelerating to the target speed n1 after the spindle has stopped is less than the energy consumption of the spindle which maintained the original speed n0 rotation, and the original speed n0 is equal to the target speed n1; where the equation is given as follows: {tI>tmintI(PSR(n1)+PB)>(tI−tT)PB+ET where t I denotes the time between two machining operations, s; t min the critical point for spindle standstill to save energy, s; P SR (n1) the spindle rotational power at spindle speed n1, W; n1 the target speed of the spindle rotational acceleration, rpm; P B the power output of the machine base module, W; t T the transient process time of the spindle rotational acceleration, which is the sum of the process time for the spindle rotational acceleration t T1and the process time for the spindle rotation transition t T2 results in, s; E T the transient process energy consumption of the spindle system, J; Step 5, the critical point in time for spindle standstill to save energy in the NC machine tool system, meets the following conditions: (1) The critical time for stopping the spindle to save energy is greater than or equal to the time for the transient process acceleration of the spindle rotation; (2) Within the critical time t min The energy consumption during the process of the spindle being stationary for a period of time and restarting and accelerating to the target speed n1 is equal to the energy consumption during which the spindle maintained the original rotational speed n0, and the original rotational speed n0 is equal to the target rotational speed n1; where the equation is given as follows: {tmin≥tTtmin(PSR(n1)+PB)=(tmin−tT)PB+ET where t min denotes the critical point in time when the spindle stops to save energy, s; t T the time of the transient process for accelerating the spindle rotation, which is the sum of the time t T1 to accelerate the spindle rotation process and the time t T2 for the transition of the spindle rotation is, s; P SR (n1) the power of the spindle rotation at spindle speed n1, W; P B the power of the basic module of the machine tool, W; E T the energy consumption of the transient process of the spindle system, J; Step 6, the critical point in time for energy saving through standstill of the spindle of the NC machine tool, can be calculated as follows: tmin=12tTI2(ASR30απ+Tsα)+tT1BSR+12tT2[ASR(30αtT1π+n1)+TsαtT1+2BSR]ASRn1+BSR where t T1 denotes the time of the spindle rotation acceleration process, s; ASR the coefficient of the primary term of the formula for spindle rotation power; α the angular acceleration of the spindle rotation acceleration process, rad / s 2 ; T S the acceleration torque of the spindle rotation acceleration, N·m; B SR the constant term of the formula for spindle rotation power; t T2 the time of the spindle rotation transition process, s; n1 the target speed of the spindle rotation acceleration, r / min; Step 7, the energy saving achieved through the energy-saving method of the NC machine tool's spindle system by means of standstill of rotation, is calculated as follows: ESA=tI(PSR(n1)+PB)−(tI−tT)PB−ET where E SA The energy saved through the energy-saving procedure involving standstill is denoted as W; t I the time between two machining operations, s; P SR(n1) the spindle rotational power at spindle speed n1, W; n1 the target speed for the spindle rotational acceleration, rpm; P B the power of the basic module of the machine tool, W; t T the time for the transient acceleration of the spindle rotation, which is the sum of the time for the acceleration of the spindle rotation t T1 and the time for the transition of the spindle rotation t T2 composes, s; E T the energy consumption of the transient spindle system, J; which is further represented as follows: ESA=(tI−tmin)PSR(n1) where t I denotes the time between two machining operations, s; t min the critical point for spindle standstill to save energy, s; P SR (n1) the spindle rotational power at spindle speed n1, W; n1 the target speed for the spindle rotational acceleration, r / min. [2] Method for determining a critical point in time for energy saving for the standstill of the spindle of an NC machine tool and method for energy saving according to claim 1, characterized by , that in step 3 the angular acceleration α and the acceleration torque T s during the acceleration of the spindle rotation by an experiment to start the spindle and t T2 This can be determined by experimentally collecting and analyzing data. [3] Method for determining a critical time for energy saving for the standstill of the spindle of an NC machine tool and method for energy saving according to claim 1, characterized by , that in step 3 t T1 as follows: tT1=2π(n1−n0)60α where n1 denotes a target speed of the spindle rotational acceleration, r / min; n0 an initial speed of the spindle rotational acceleration, r / min; and α an angular acceleration of the spindle rotational acceleration process, rad / s 2 .