Optical Measuring System Optimization Test for the ballscrew

Since the ballscrew raceway profile straightforwardly influences the benefit characteristics and exactness maintenance of ball screws, this paper proposes an optimized ceaseless measuring strategy for the ballscrew raceway profile, without the have to be alter the sensor for the estimation of each raceway. Based on the comparison of existing measuring strategies and standards, an optical measuring framework is developed, in which the establishment mistake of both the Driven sensor and straight calibration framework, and the straightness of the portable stage are analyzed and gotten. More importantly, both the transformation algorithm of the helix angle and the arc-selecting principle are proposed. Compared to the measuring results and time consumption of the profilometer, the maximum error for the measured radius and contact angle of the system proposed in this paper is 1.5μm and 35′, and the measuring efficiency is increased by 15.8%, 58.6% and 67.5% for 1, 5 and 20 continuous raceways, respectively, which shows a good performance in accuracy, repeatability and efficiency. Moreover, the system is also capable of measuring the pitch diameter and lead error of ballscrew, which is significant for classifying the accuracy of the ballscrew raceway profile and improving the machining precision.

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(b) Fig. 1. Confocal laser measuring method (a) sketch of confocal laser measurement, (b) confocal laser measuring principle.

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(b) Fig. 2. Triangulation laser measuring method (a) sketch of triangulation laser measurement, (b) triangulation laser measuring principle.

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(b) Fig. 3. LED sensor measuring method (a) sketch of LED sensor measurement, (b) LED sensor measuring principle. Ball screws, which are widely used in CNC machine tools, have a great performance on reliability, rigidity and bearing capacity. The parameters of ballscrew raceway profile directly determine the load distribution in ball screws, and therefore affect the contact stiffness and friction characteristics. With the development of the modern manufacturing industry, the positioning accuracy and precision retention are becoming increasingly important, which confirms the indispensability of machining accuracy detection for ball screws. Most of the modern manufacturing companies have relied on the roughness profilometers launched by industrial measuring corporations. Measurement, the profile usually was measured along the normal section of the ballscrew raceway. Although this method can achieve relatively high accuracy, the probe must be adjusted for the measurement of each raceway. That is, it is not applicable in the batch tests due to the low efficiency, and more importantly, the surface with poor roughness is more likely to cause the probe wear. Therefore, existing non-contact measuring methods still cannot realize continuous measurement. Contact measurement is not suitable for batch tests, and non-contact measurement by the industrial camera is likely to be affected by lens distortion and image processing. Considering the accuracy of the optical measurement, three kinds of optical sensors are studied in this paper, namely confocal laser, triangular laser, and LED sensor, of which the applications and measuring principles are shown in Fig.1, Fig. 2 and Fig. 3. When using the confocal laser (Fig. 1 (a)) or triangular laser (Fig. 2(a)), to scan the 60 ballscrew raceway profile along the side generatrix, the laser should be set parallel to the Y-axis. And the two-dimensional (2D) mobile station is used to adjust the measuring distance of the sensor both along the X-axis and the Y-axis. When using the LED sensor (Fig. 3(a)), if the optical path is set parallel to the Y-axis, the projection of partial profile along upper side or lower side cannot be perceived by the receiver due to the light occlusion caused by the helical surface of the ballscrew. To avoid the image distortion and acquire the complete profile, the LED sensor should be rotated at a helix angle from the Y-axis, making the optical path consistent with the tangential direction of the helical line on the measured \raceway. To find the most suitable optical sensor, preliminary experiments were carried out.