Guide systems for moving mechanical elements.pptx

Guide systems for moving elements

1. Guide systems for moving elements: Tool Rest and Workpiece By: Sneha Pandey 1902111053

2. Elastic hinge or spring guide C omposed of an elastic element lying between two solid moving elements. The guiding action is performed by deformation of the elastic element, which is called an elastic hinge or spring guide. In this system, the friction accompanying relative transfer motion of the moving elements is removed, except for the internal friction of the elastic material. Also there is no backlash in the mechanism joining the elastic element and the two moving elements.

3. Linear slide guide The system is basically sliding of two solid surfaces in contact, but there is always stick-and-slip motion. To avoid friction effects, lubricants are used in general, but in microfine motion, boundary lubrication is always used. The guide surface should be finished to sub- nanometre order because the oil may be degraded by a rough surface. Solid powder lubricants as MoS2 and graphite cannot be used for such guide systems, because shear slip of these powders is not very stable. Slide guide systems of nanometre accuracy are effectively realized by lubrication with oil of high oiliness and guide surfaces of sub- nanometre roughness.

4. Linear roller bearing The relative motion of moving elements through rolling elements such as balls, rollers and needles is effectively achieved in many accurate mechanisms. In order to realize motion of nanometre accuracy, it is necessary to maintain the geometrical accuracy of rolling elements: the maximum eccentricities and diametral accuracies of the balls and rollers must be 10 nm and 50 nm respectively. The ball screw V groove guide mechanisms shown in Fig. 3.1.4 are of great use, but there is always a relatively large spinning friction between ball and guide race. Therefore they always show stick-and-slip phenomena due to driving force and transfer, and also a relatively large backlash due to erratic geometrical form. Another mechanism, using a knife edge with sharp edges interfaced between two moving elements, is shown in Fig. 3.1.5. This mechanism, with a hardened knife edge and agate bearing, has been developed as a very accurate supporting system for microbalances.

5. LINEAR SLIDE GUIDE

6. Hydrostatic slide guide Hydrostatic slides have been successfully applied to ultra-precision machine tools because of some attractive characteristics, such as high accuracy, high stiffness and damping, low friction torque, and absence of wear. In the configurations of hydrostatic slides shown in Fig. 3.1.7(a) and (b), pressurized liquid has to be fed to the table through pipes, and these pipes can sometimes disturb the precise motion of the table.

7. Hydrostatic slide guide Figures 3.1.9 and 3.1.10 show new types of hydrostatic slides which can achieve a very high stiffness using self-controlled restrictors. The self controlled restrictor shown in Fig. 3.1.9(a )(4 ) uses the elastic deformation of a diaphragm to control liquid ffow entering the slide, while the one shown in Fig. 3.1.10(a) uses a floating disk and controls the liquid- fow by using the force balance acting on the upper and lower sides of the disk. Figures 3.1.9(b) and 3.1.10(6) show the relations between liquid film thickness and applied load.

8. Hydrostatic journal bearing Like hydrostatic slides, hydrostatic journal bearings have vaious advantages for ultra-precision machine. Figure 3.1.11 shows typical configurations of hydrostatic journal bearings. The bearing shown in Fig. 3.1.11(a) is an ordinary bearing which has several pockets and restrictors inside the pockets. The bearing shown in Fig. 3.1.11(6)° has drain holes inside the pockets, and a wider range of design conditions can be selected by changing the diameter of the drain holes.

9. Hydrostatic journal bearing Hybrid bearings can achieve a higher stiffness by using the hydrodynamic effect, but they also have some disadvantages such as higher power consump - tion and higher temperature rise under the rotating condition. To overcome these disadvantages in hybrid bearings, hydrostatic journal bearings with self controlled restrictors have therefore been proposed. Figure 3.1.13 shows an example of a hydrostat1c journal bearing with a self-controlled restrictor.

10. EXPECTED QUESTIONS Briefly explain about elastic hinge or spring guide. Explain the difference between linear slide guide and hydrostatic slide guide. Explain the difference between linear roller bearing and hydrostatic journal bearing.

11. THANKYOU!