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

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

• using two temperature sensors;
• wherein, using one of the temperature sensors to determine temperature of an upper surface of spindle box, and using the other temperature sensor to determine temperature of a lower surface of the spindle box;
• drawing the thermal error-temperature loop based on the radial thermal drift error of the spindle and temperature difference between the upper surface and the lower surface of the spindle box;
• analyzing mechanism of radial thermal deformation of the spindle based on the thermal error-temperature loop in order to evaluate a level of the radial thermal errors;
• wherein steps of evaluating the level of the radial thermal errors are as follows:
• (1) arranging one of the temperature sensors on each of the upper surface of the spindle box and arranging the other temperature sensor on the lower surface of the spindle box, respectively;
• wherein the temperature sensor arranged on the upper surface of the spindle box is T1 and the other temperature sensor arranged on the lower surface of the spindle box is T2;
• (2) determining the radial thermal drift error along X- and Y-directions of the spindle by utilizing the bar and the two displacement sensors;
• selecting a direction corresponding to a high value of the radial thermal drift error;
• determining the radial thermal drift error of the spindle using the bar and the two displacement sensors arranged along a spindle axis;
• wherein the displacement sensor near a nose of the spindle is P2 and the other displacement sensor is P1;
• setting a test direction of the displacement sensors:
• the bar moves away from the displacement sensors as the radial thermal drift error increases;
• (3) test procedures for the radial thermal errors and temperature are as follows:
• letting the spindle initially run for M hours at a certain speed, and then stopping the run and letting the spindle remain at rest for N hours;
• determining a total test time as M+N hours;
• recoding data of the two temperature sensors during the test for the radial thermal errors of the spindle;
• (4) letting two groups of temperature data measured by the temperature sensors T1 and T2 be t1 and t2, respectively;
• letting two groups of displacement data measured by the displacement sensors P1 and P2 be e1 and e2, respectively;
• calculating the temperature difference ΔT between T1 and T2 using the formula:
• ΔT(1)=[t1(1)]−[t2(1)−t2(1)], i=1,2, . . . ,n (1)
• drawing a curve that is the thermal error-temperature loop with ΔT as abscissa and e1 as ordinate;
• (5) analyzing the radial thermal deformation of the spindle and evaluating the level of the radial thermal errors of the spindle based on the thermal error-temperature loop;
• evaluating the level of the radial thermal errors of the spindle is as follows:
• a) the larger the size of the thermal error-temperature loop is, the larger a radial thermal tilt and a radial thermal drift of the spindle are;
• b) the flatter the thermal error-temperature loop in a lateral direction is, the larger the radial thermal drift of the spindle is, and the smaller the radial thermal tilt of the spindle is;
• c) the flatter the thermal error-temperature loop in a longitudinal direction is, the larger the radial thermal tilt of the spindle is, and the smaller the radial thermal drift of the spindle is.