Application method of the thermal error-temperature loop in the spindle of a cnc machine tool

An application method of the thermal error-temperature loop in the spindle of a CNC machine tool, wherein a bar and two displacement sensors are initially used to determine the radial thermal errors of the spindle, which include thermal drift error and thermal tilt error;

• meanwhile, two temperature sensors are used to determine the temperature of the upper and lower surfaces of the spindle box;
• then, based on the radial thermal drift error of the spindle and the temperature difference between the upper and lower surfaces of the spindle box, the thermal error-temperature loop is drawn;
• finally, the mechanism of the radial thermal deformation of the spindle is analyzed based on the thermal error-temperature loop so that the level of the thermal error can be evaluated;
• wherein the steps are as follows:
• (1) arranging one temperature sensor on each of the upper and lower surfaces of the spindle box respectively;
• the temperature sensor near the surface of the spindle motor is T1 and the other temperature sensor is T2;
• (2) determining the radial thermal drift error along the X- and Y-directions of the spindle by utilizing a bar and two displacement sensors;
• selecting a direction with higher radial thermal drift error;
• then, using the bar and two displacement sensors arranged along the spindle axis to determine its thermal error;
• the displacement sensor near the nose of the spindle is P2 and the other one is P1;
• the test direction of the displacement sensor is set as:
• the bar moves away from the displacement sensors along with the radial thermal drift error increasing;
• (3) the test procedure for the thermal error and temperature:
• the spindle initially runs for M hours at a certain speed and then the spindle stops running and remains at rest for N hours;
• therefore, the total test time is M+N hours;
• recoding the data of two temperature sensors during the test for the radial thermal error of the spindle;
• (4) letting two groups of temperature data measured by temperature sensors T1 and T2 be t1 and t2;
• letting two groups of displacement data measured by displacement sensors P1 and P2 be e1 and e2;
• the formula for calculating the temperature difference ΔT between T1 and T2 is as follow:
• ΔT(i)=[t1(i)−t1(1)]−[t2(i)−t2(1)],i=1,2, . . . ,n (1)
• the curve drawn with ΔT as the abscissa and e1 as the ordinate is approximately a loop, which is called the thermal error-temperature loop;
• (5) based on the thermal error-temperature loop, the radial thermal deformation of the spindle is analyzed and the radial thermal error level of the spindle is evaluated;
• the evaluation method is as the following:
• a) the bigger the size of the thermal error-temperature loop is, the greater the radial thermal tilt and the thermal drift of the spindle are;
• b) the flatter the thermal error-temperature loop in the lateral direction is, the lager the radial thermal drift of the spindle is, and the smaller the thermal tilt is;
• c) the flatter the thermal error-temperature loop in the longitudinal direction is, the larger the radial thermal tilt of the spindle is, and the smaller the thermal drift is.