MECHANICAL DEVICES AND STRUCTURES

Abstract: In a mechanical structure having a pair of co-operating components separated by a layer of vibration-damping material, the geometry of surfaces constituting the interface between the components is adapted so that the damping material will inhibit vibrations of the components. The damping material may be air or other fluid between a longitudinal tongue (18A) of a component (18) and a longitudinal groove (18B) of a component (17) on which the component (18) is linearly slidable; or between a driven rotary spindle (15A) and a bearing stator (15B) in which it is mounted, and in an annular space (15D) between the stator (15B), and an annular extension (15C) thereof, and the surrounding body of a tool holder (9) in which the stator (15B) is mounted.

Description: MECHANICAL DEVICES AND STRUCTURES This invention relates to mechanical devices and structures, and in particular to the damping of vibrations therein. Especially in connection with the mounting and guidance of precision tools or measuring instruments, for example, it is desirable not only to provide a rigid precision mounting v structure but also to minimise the effects of vibration either generated by or transmitted to the tool or instrument. It is found that this object can be achieved by the provision of a layer of damping material between suitably shaped spaced surfaces of adjacent components of the mounting structure. According to the present invention there is provided a mechanical structure having a pair of cooperating components separated by a layer of vibration-damping material, wherein the geometry of the interface between said components is adapted so that said damping material will inhibit vibrations of said components. In one embodiment of a structure according to the invention, the said components are mounted for rectilinear motion relative to one another and are formed with mutually opposed surfaces, for example plane surfaces, extending parallel to the direction of such relative motion with the said damping material disposed in a clearance between them. In another embodiment, the said components are mounted for rotation, relative to one another, about an axis of rotation, and are formed with mutually opposed surfaces, for example cylindrical surfaces, which are surfaces of rotation about that axis and which have the said damping material disposed in a clearance between them. The invention will be more fully understood from the following description of embodiments thereof with reference to the accompanying drawings, in which:- Figure 1 is a front elevational view of a tetrahedral mounting device for a machine tool, a modification of an embodiment of the tool described in U.K. Patent Application No.2194182A; Figure 2 is a lateral sectional view, on the line II—II of Figure 1, of the mounting device and machine tool shown in Figure 1 ; Figure 3 is a section, on a larger scale, through a workpiece mounting table for the machine tool; and Figure 4 is a section, on a larger scale, through a toolholder shown in Figures 1 and 2. The tetrahedral mounting structure shown in Figures 1 and 2, which is as described and claimed in UK Patent Application No. 2194182A, includes six rod-like members la - If. Each member comprises a tubular outer strut 2a - 2f enclosing a tensile rod 3a - 3f. At each apex of the tetrahedral structure is a hollow sphere 4a - 4d. Each sphere comprises a pair of mating hemispheres 5a - 5d, 6a - 6d. The halves of the hemispheres are held together by threaded bolts 7. Each sphere abuts the outer strut of three of the rod-like members and is clamped thereto by means of bolts 8 attached to the ends of the corresponding enclosed tensile rod. Mounted on the rod-like members la, lb and lc which are remote from the base constituted by members Id, le and If is a machine tool holder 9. The machine tool holder is clamped to rod-like members la, lb and lc by means of threaded bolts 10 and space blocks 11. The machine tool holder 9 and the hollow sphere 4d have respective bores 12 and 21, coaxial with the machine principal axis 13, through which passes a drive shaft 14 carrying an air bearing spindle having a rotor 15A and a stator 15B and a grinding tool 16, as shown in Figure 2 and (on a larger scale) in Figure 4. The stator has an extension 15C to provide an extended viscous damping workface 15D. Mounted on the base rod-like members Id, le and If is a vee slideway 17 bearing a workpiece holder 18 to impart linear motion to a workpiece 19 beneath the grinding tool 16. The workpiece holder is provided with a dividing strip 18A. Interfaces 18B are provided with a viscous damping medium. The slideway has a hollowed-out portion 20 so that the wall thickness is similar to that of the other structural components. The hollow sphere remote from the base contains a bore 21 through which the drive shaft passes. On the areas between the dividing strip of the sliding workpiece holder 18 and the matching slot in the vee slideway 17 and between the stator of the air bearing rotary spindle 15 and the bore of the machine tool holder 9, there is relative motion, the viscous drag of the damping medium being arranged to be insignificant for the rate of motion required. The geometry of the damping interface can be matched to the modes of the vibration expected or most needing attenuation, for instance the plane vertical damping interfaces between the driving strip of the sliding workpiece holder 18 and the matching slot in the vee slideway 17 will respond efficiently to horizontal mode vibrations from the drive to the sliding workpiece holder and the principal axis (vertical) vibrations; whereas the cylindrical damping interface between the stator of the air bearing rotary spindle 15 and the bore of the machine tool holder 9 will respond efficiently to torsional vibrations from the rotary spindle and to principal axis (vertical) vibrations. Similarly, appropriate vibrational damping may be provided in the spherical coupling between the drive shaft 14 and the rotor 15A. It has been found that the thickness of the viscous damping layer (i.e. the gap between the solid surfaces thus comprising the damping interface) can be 50 micrometres or greater with suitably high-viscosity damping fluids, so that no tribological (fretting, pick up, wear) problems will arise with dimensional tolerances within normal engineering practice. Close proximity of the two surfaces, as on some existing machines, is not needed; this again avoids tribological problems, and the inconsistent vibration damping which frequently results from stick-slip when the two surfaces are in close proximity or intermittent contact.

Claims: CLAIMS 1. A mechanical structure having a pair of co-operating components separated by a layer of vibration-damping material, wherein the geometry of the surfaces constituting the interface between said components is adapted so that said damping material will inhibit vibrations of said components. 2. A structure as claimed in Claim 1, wherein the said ' components are mounted for rectilinear motion relative to one another and are formed with mutually opposed surfaces extending parallel to the direction of such relative motion with the said damping material disposed in a clearance between them. 3. A structure as claimed in Claim 2, wherein the mutually opposed surfaces comprise mutually opposed plane surfaces. 4. A structure as claimed in Claim 1, wherein the said components are mounted for rotation, relative to one another, about an axis of rotation, and are formed with mutually opposed surfaces which are surfaces of rotation about that axis and which have the said damping material disposed in a clearance between them. 5. A structure as claimed in Claim 4, wherein the mutually opposed surfaces comprise mutually opposed cylindrical surfaces. 6. A structure as claimed in any of the preceding claims, wherein the surfaces constituting the said interface are separated by a distance of at least 50 micrometres and the damping material between them is a high-viscosity fluid. 7. A mechanical structure with vibration damping provision, substantially as described herein with reference to the accompanying drawings.

Inventors: LINDSEY KEVIN, LINDSEY, KEVIN
Applicants: NAT RES DEV, NATIONAL RESEARCH DEVELOPMENT CORPORATION
Application year: 1989
Main classification: B23Q1
IPC codes: B23Q1, B23Q11, F16C29, F16F15