LM Guide THK - Industrial Technologies

Индастриал Технолоджис www.industrial‐technologies.com.ua +38 044 498 21 94Four Raceway, Circular-Arc Groove,Two-Point Contact StructureSince the ball contacts the groove at two points in theload direction as shown in Fig.12 and Fig.13 on A1-15even under a preload or a normal load, the differencebetween d1 and d2 is small and the differential slip isminimized to allow smooth rolling motion.In the ideal two-point contact structure, four rows ofcircular arc grooves are given appropriate contactangles. With this structure, a light distortion of themounting surface would be absorbed within the LMblock due to elastic deformation of the balls and movingof the contact points to allow unforced, smoothmotion. This eliminates the need for a robust mountingbase with high rigidity and accuracy for machinerysuch as a conveyance system.With the two-point contact, even if a relatively largepreload is applied, the rolling resistance does notabnormally increase and high rigidity is obtained.Since the curvature radius of the ball raceway is 51 to52% of the ball diameter, a large rated load can beobtained.Smooth MotionAccuracy and Rigidity of the Mounting SurfaceRigidityLoad RatingDifference in RigidityTwo-Row, Gothic-Arch Groove,Four Point Contact StructureThe difference between d1 and d2 in the contact area islarge as shown in Fig.12 and Fig.13 on A1-15. Therefore,if any of the following occurs, the ball will generatedifferential slip, causing friction almost as large assliding resistance and shortening the service as aresult of abnormal friction.(1) A preload is applied.(2) A lateral load is applied.(3) The mounting parallelism between the two axesis poor.With the Gothic-arch groove product, each ball contactsthe groove at four points, preventing itself frombeing elastically deformed and the contact points frommoving (i.e., no self-adjusting capability). Therefore,even a slight distortion of the mounting surface or anaccuracy error of the rail bed cannot be absorbed andsmooth motion cannot be achieved. Accordingly, it isnecessary to machine a highly rigid mounting basewith high precision and mount a high precision rail.Since differential slip occurs due to the four-point contact,a sufficient preload cannot be applied and highrigidity cannot be obtained.Since the curvature radius of the gothic arch groovehas to be 55 to 60% of the ball diameter, the rated loadis reduced to approx. 50% of that of the circular arcgroove.As shown in Fig.14, the rigidity widely varies according to the difference in curvature radius or difference in preload.Curvature radius and rigidityComparison of rigidity by curvature(per ball)108642Ball diameter (mm)R=0.6DaR=0.55DaR=0.52Da0 2 4 6 8 10 12Rigidity (N/μm)Fig.14Difference in Service LifePreload and deflectionDisplacement curve of HSR30600 clearanceMagnitude of the preload: 5kN10 20Applied load (kN)Since the load rating of the gothic arch groove is reduced to approx. 50% of that of the circular arc groove, theservice life also decreases to 87.5%.Deflection (Rigidity) (μm)40200Industrial TechnologiesA1-16