GB2194182A

GB2194182A - Mounting devices

Info

Publication number: GB2194182A
Application number: GB08719169A
Authority: GB
Inventors: Kevin Lindsey
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-08-13
Filing date: 1987-08-13
Publication date: 1988-03-02
Anticipated expiration: 2007-08-13
Also published as: EP0256853B1; GB8619699D0; US4872291A; DE3766444D1; JPS6374540A; EP0256853A1; JP2583520B2; GB2194182B; GB8719169D0; SU1671154A3

Description

GB2194182A 1

SPECIFICATION filled with a damping material.

The structural members can thus be tuned Mounting devices to produce minimum excitation of each other and the smallest interception of the wide This invention relates to mounting devices and 70 spectrum of destabilising sources.

in particular to mounting devices having high A regular (equilateral) tetrahedral structure inherent rigidity and being suitable for high may be constructed so that all members are precision machine tool and metrological appli- dimensionally, physically and mechanically sub cations. stantially identical with advantageous effects Conventional machine tools comprise three- 75 on the structure's physical and mechanical or four-cantilever systems with, for example, a properties (stiffness, vibration response, ther base or work head, and a post and tool mal characteristics).

bracket. Examples are a vertical axis grinder, a Although a regular tetrahedral structure is drill and a horizontal axis lathe With such substantially symmetrical about four axes, for structures the cross-sectional area of the con- 80 most applications it is sufficient to consider stituent components needs to be large to ob- symmetry about an axis normal to a triangular tain acceptable rigidity. face through the vertex not contained in that We have found that improved rigidity and face. This axis will hereinafter be referred to reduced sensitivity to thermal and other desta- as the machine principal axis and the surface bilising forces can be attained by adopting a 85 normal thereto as the base.

tetrahedral mounting structure. The inherent axial symmetry of a tetrahedral Accordingly the present invention provides a structure means that, for a homogeneous ther- mounting device comprising six rod-like memmal input, no structural distortion results, only bers the ends of which are rigidly coupled a predictable dimensional increase. Because of together to form a substantially tetrahedral 90 the symmetry, and if all components have the structure and mounting means comprising a same thermal expansivity and the same ther rigid member fixedly coupled to three of said mal response, the relative positions of two rod-like members, said three rod-like members points immediately adjacent to one another, not being co-planar. but not directly coupled, (for example, a tool A structure formed from rod-like members, 95 and a workpiece) will not alter with changing for example, bars, rods or tubes, will show no temperature. A tetrahedral mounting device is tendency to shape distortion or shearing by therefore automatically thermally compensated.

the application of a tensile or compressive (This is strictly true only if the workpiece is of stress to the apices if all of the apices are the same material as the machine or if the connected by straight members. (The only dis- 100 specimen is positioned with respect to the tortion is that produced by the relatively small mounting device at the workpiece working elastic compression or extension of the face; however, in practice, even in the former straight member) Without these directly-joining case, the departure from complete compensa members the apices will tend to suffer rota- tion can be very small).

tion (if pin-jointed) and if rigidly connected will 105 Components such as rotary motions, linear tend to bend the straight members. An optimotions, workpieces, tools, can be added to mal structure is a tetrahedron which, having the tetrahedron usually without significantly only four joints, the minimum necessary for a compromising its major attributes; some can three dimensional framework, has few distor- even be beneficial. An example is the addition tion modes Intrinsical ly, a tetrahedron has a 110 of a bracket which is inside the working vol straight member connecting each of its apices. ume, symmetrical about the machine axis, par- Since a tetrahedron can be pin-jointed, the allel to the machine base and fixed symmetri- members can be decoupled so that vibration cally (at the centres) to the three _upright is not transmitted. Vibrations are therefore co- members. This bridge will show no tendency nfined to individual members. Susceptibility to 115 to joint rotation, etc. because the three up vibration is decreased by maximising the fun- rights forming part of the bridge cannot shear.

damental frequencies of the components of The fixing of this bracket/bridge to the the structure. This can be achieved by using centres of the three uprights reduces the ef low aspect ratio (ratio of length to diameter/- fective length, and increases the fundamental width) components and, in the case of tubular 120 frequency of the uprights thus making them members, by optimising wall thickness. The statically and dynamically stiffer.

enclosed space in tubular members can be Similarly a bracket/bridge mounted symmet- utilised to assist with vibration desensitisation rically across the base will stiffen it in one in two ways It may contain an adjustable ten- plane at least-this stiffening can be en sioning rod/screw system to tune the tubular 125 hanced in other planes by extra joining of member s fundamental frequency. It may also member's centres-all without encroaching be used to contain rods which have funda- upon the machine working volume. Thus the mental frequencies different from that of the tetrahedron s major attributes are not com tubular member. Additionally the gap between promised by the addition of axially symmetri the rods and the tubular members may be 130 cal accessories. The self- contained tension/- 2 GB2194182A 2 compression adjusting feature of the structural substantially identical dimensions as are the members can be used to balance up the effect remaining three. The rod- like members of the of the accessories masses on structural funda- two groups are not necessarily of the same mental frequencies, etc. dimensions. In such a case an isosceles rather A specific embodiment of the invention will 70 than an equilateral structure will result.

now be particularly described by way of Preferably machining or other activity is per- example with reference to the accompanying formed in the vicinity of the principal machine drawings in which:- axis to minimise distortion effects.

Figure 1 is a partially cut-away plan view of Other forms of slideway may be employed.

a tetrahedral mounting device for a machine 75 Preferably the linear motion slideway and spe tool; cimen carrier are connected to drive means at Figure 2 is a front elevational view of this the centre of friction of the slideway.

device in the direction indicated by the arrow It is not essential to employ mounting 1 A on Figure 1; spheres at the apices of the tetrahedral struc- 1 Figure 3 is a side elevational view in the 80 ture. A solid hinge comprising a weld contact di ection indicated by the arrow B on Figure or pin joint just sufficient to give static stiff 1; ness may be used instead.

Figure 4 is a sectional view -along the line Additional stiffness may be applied to the CC; and Figure 5 is a detailed section of a base rod-like members by an extra tube mounting arrangement Referring now to the 85 screwed or stuck on to the underside.

drawings, a tetrahedral mounting structure in- Advantageously, vibration damping may be cludes six rod-like members la-1f. Each introduced at mounting decoupling points.

member comprises a tubular outer strut The use of mounting devices is not limited 2a-2f enclosing a tensile rod 3a-3f. At to machine tools It may be used in any appli each apex of the tetrahedral structure is a holcation, such as surface metrology where a low sphere 4a-4d. Each sphere comprises a high degree of stiffness and rigidity is re pair of mating hemispheres 5a-5d, 6a-6d. quired.

The halves of the hemispheres are held to- Furthermore, a small degree of frustration of gether by threaded bolts 7. Each sphere abuts the tetrahedral structure is contemplated in the outer strut of three of the rod-like mem- 95 some applications, for example, to facilitiate bers and is clamped thereto by means of apical mounting of subsidiary structures.

bolts 8 attached to the ends of the corre

Claims

sponding enclosed tensile rod. Mounted on CLAIMS the rod-like members

remote from the base is 1. A mounting device comprising six rod-like a machine tool holder 9 The machine tool hol- 100 members the ends of which are rigidly coup der is clamped to rod-like members by means led together to form a substantially tetrahedral of threaded bolts 10 and space blocks 11. structure and mounting means comprising a The mounting is non-kinematic thereby impart- rigid member fixedly coupled to three of said ing greater rigidity. The machine tool holder rod-like members, said three rod-like members has a hole 12 coaxial with the machine princinot being co-planar.

pal axis 13 through which passes a drive
2. A mounting device as claimed in claim 1 shaft 14 carrying an air bearing rotary spindle wherein said rod-i;ke members are arranged in and a grinding tool 16. Mounted on the two groups of three the members of each base rod-like members is a vee slideway 17 group being of substantially equal dimensions bearing a workpiece holder 18 to impart linear 110 to one another.

motion to a workpiece 19 beneath the grind-
3. A mounting device as claimed in claim 2 ing to 1 16 The slideway has a hollowed-out wherein all said rod-like members are of sub- _Y portion 20 so that the wall thickness is similar stantially equal dimensions to one another.

to that of the other structural components.
4. A mounting device as claimed in any one The hollow sphere remote from the base con- 115 of the preceding claims wherein said rod-like tains a bore 21 through which the drive shaft members are coupled by means of substan passes. tially spherical hollow members.

The ends of the tensile rods do not abut
5. A mounting device as claimed in claim 4 the apical spheres. This is to permit the reso- wherein each hollow member comprises a pair nance of the rods to be tuned by adjusting 120 of mating hemispheres.

the screws 8 so that it differs from the reso-
6. A mounting device as claimed in any one nant frequency of the tubular struts 2a-2f. of claims 1 to 3 wherein said rod-like mem- The interface between the tensile rods and bers are coupled together by means of a the tubular ou ter struts may comprise a vis- welded contact.

cous fluid for Coulomb friction damping. 125
7. A mounting device as claimed in any one Preferably all components are made from of claims 1 to 3 wherein said rod- like mem- material with the same expansivity and similar bers are coupled together by means of a pin cross-section to equalise thermal response joint.

rates.
8. A mounting device as claimed in any one The rod-like members are preferably all of 130 of the preceding claims wherein decoupling 3 GB2194182A 3 means is provided between said rod-like mem bers to inhibit the transmission of vibrations.
9. A mounting device as claimed in any one of the preceding claims wherein susceptibility to vibration is decreased by maximising the fundamental frequencies of the components of the device by using low aspect ratio compo nents.
10. A mounting device as claimed in any one of the preceding claims wherein said rod like members are of two-part construction comprising a strut member and a tensile mem ber.
11. A mounting device as claimed in claim 10 wherein said rod-like member includes a tubular member having a tensile rod there through.
12. A mounting device as claimed in claim where.in at least two of said rod-like mem bers have a different fundamental frequency of vibration.
13. A mounting device as claimed in claim 12 wherein at least one of said tensile rods is provided with an adjusting screw system to tune the corresponding tubular members fun damental frequency of vibration.
14. A mounting device as claimed in claim 12 wherein at least one of said tubular mem bers is provided with viscous damping ma terial between the tubular member and the tensile rod.
15. A mounting device as claimed in any ony of the preceding claims wherein the mounting means is non-kinematically coupled to said three rod-like members.
16. A mounting device as claimed in any one of the preceding claims having additional stiffening means attached to the rod-like mem bers.
17. A mounting device substantially as herein described with reference to and as shown in the accompanying drawings.
18. A machine tool' incorporating a mount- ing device as claimed- in any one of the pre ceding claims.
19. A measuring instrument incorporating a mounting device as claimed in any one of the preceding claims 1 to 17.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sites Branch, St Mary Cray, Orpington, Kent BF15 3RD.

Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.