US 3272568 A
Description (OCR text may contain errors)
p 1966 J. KOORNEEF ETAL 3,272,568
GUIDING DEVICES Filed July 9, 1963 5 Sheets-Sheet l PRIOR ART T J 3 flull TIJMiL F q |n|. m
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5 Sheets-Sheet 5 AMPLIFIER RECTIFIER GUIDING DEVICES J- KOORNEEF ETAL DIFFERENTIAL AMPLIFIER WHEATSTONE BRIDGE Sept. 13, 1966 Filed July 9, 1963 INVENTOR. IIIIIII R T N E G A SOFT FERROXDUR SOFT STEEL United States Patent 3,272,568 0 GUIDHNG DEVICE .l'acoh Koorneef, Emmasingel, Eindhoven, Netherlands, Simon Duinker, Hamburg, Germany, and George Ludwig Walther, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Line, New York, N.Y., a corporation of Delaware Filed July 9, 1963, Ser. No. 295,282 Claims priority, application Netherlands, Mar. 28, 1962 276,532 9 (Jlaiins. (Cl. 308-) This application is a continuation in part of my copending application Serial No. 267,257, now abandoned, filed March 22, 1963.
The invention relates to a guiding means comprising a fixed guide member and a guided body adapted to move relative thereto, and means for maintaining an air or gas cushion between the opposed surfaces of the fixed and movable parts. In the known guiding devices the guide surfaces are separated from each other by a gas cushion, so that the frictional forces existing between such surfaces are practically negligible. The parts of such a guiding device are therefore readily movable relatively to each other. The gas cushion, an eificient thickness of which may be 10 microns, has the further adgiantage that it is unnecessary to lubricate the guide suraces.
Particularly with precision tools, for example, machine tools, it is necessary that the thickness of the gas cushion be as constant as possible. If the guide member is horizontally arranged, the body which is movable with respect to the guide member and supported on the air cushion can be loaded with a given weight so that the gas cushion is, so to say, biased and the cushion thickness maintained constant. By choosing a heavy total weight bearing on the gas cushion with respect to the load imposed by the cutting tool said constancy can be achieved to a reasonable extent. In practice, this requires fairly heavy weights. For example, a bias weight on the gas cushion of 100 kgs. is required for maintaining a reasonable constant thickness of the gas cushion with a variation of 1 kg. in the tool load.
Prestressing the gas cushion by means of a weight has the disadvantage that the weight required may give rise to undesirable bending of the guide member. A further disadvantage of prestressinga gas cushion by weights is that this is only possible, with substantially horizontal disposed guiding surfaces. Consequently, if the guide surfaces are in a position deviating markedly from the horizontal, said solution is ineffective. A further disadvantage is that heavy weights for prestressing the gas cushion give rise to comparatively great inertial forces with rapidly reciprocating parts.
According to this invention a guiding system is provided which has none of the above noted disadvantages.
The guiding device according to this invention is characterized in that at least one of the relatively movable parts is provided with one or more magnets for drawing this part and an, at least partially ferromagnetic, opposite part of the guiding device towards each other thereby prestressing the gas cushion separating the parts. It is thus possible, in spite of the low natural weight of the magnets, to obtain a bias force of the required value. With such a guiding system, operation is independent of the physical disposition of the guide member, i.e. horizontal or vertical position, since irrespective of the position of the guide surfaces the magnets can constantly draw the relatively movable parts of the device towards each other. It has furthermore been found that the magnets provide rapid damping of oscillations in the device by virtue of the eddy currents produced by the magnets. A further advantage of the use of magnets for obtaining 3,2725% Patented Sept. 13, 1966 the required bias force on the gas cushion is provided in that comparatively light-weight structures may be utilized. Additionally, these structures may be compact, so that they may be employed advantageously with those precision tools, in which space plays an important part,
The system briefly described above may be applied to many types of guiding devices. Examples thereof are the guiding devices in which the guide surfaces are relatively rotatable or slidable along a rectilinear or curved path. The guide surfaces themselves may be curved or flat.
In a further embodiment of the guiding device according to the invention, two guide surfaces are arranged at an angle to each other on one part in cooperation with two corresponding guide surfaces arranged at the same angle on an opposite part and magnets are provided in at least one of the relatively movable parts, which act on each of the adjacent angularly related guide surfaces. In this case only two guide surfaces, arranged at a given angle to each other, both on the body and on the guide path, will suffice, which (in contrast to the dovetail guide member heretobefore used for precision tools and made at fairly high costs) can be manufactured at substantially reduced expense. If, for example, the two guide surfaces arranged at an angle to each other are formed by a pair of horizontal guide surfaces and a pair of vertical guide surfaces, and having magnetic attraction forces acting there-between no further measures are required to maintain operative relationship between the parts.
In order to ensure a constant thickness of the gas cushion, use may be made, as stated above, of prestressing forces which are high as compared with the variation in the force of a tool load, forexample, directed towards the guide surfaces. However, use may be made of a prestressing force which is lower, if the prestressing force is provided by variable electro-magnetic means (FIGS. 11, 12, 13) controlled by any suitable apparatus which measures the thickness of the gas cushion between cooperating guide surfaces and varies the energizing current of the electro-magnets with a variation of the thickness measured.
Although the magnets, which may be permanent or electro-magnets, may be arranged in one or in both relatively movable guide parts of the device, it is preferred,
with a view to the stability in the relative movement of the guide surfaces, to arrange the magnets in the smaller and/ or movable member of the cooperating parts and acting on the associated guide surfaces.
The invention will now be described more fully with reference to the drawing, which shows schematically a few presently preferred embodiments.
In FIG. 1 the main parts of a known guiding device are diagrammatically illustrated, in which a gas cushion is maintained between the guide surfaces.
FIG. 2 shows an arrangement similar to that of FIG. 1, but provided with magnets in accordance with the invention.
FIGS. 3 and 4 are a plan view and a sectional view respectively taken on the line IVIV in FIG. 3, of a rectilinear guide system according to the invention.
FIG. 5 shows a variant of the arrangement of FIG. 3, comprising a curved guide path.
FIGS. 6 and 7 illustrate theease with which the rectilinear guide shown in FIGS. 3 and 4 is manufactured.
FIGS. 8 and 9 show a rectilinear guide system in which a long sledge or bed of a machine is adapted to slide along two separate supporting and guiding parts; FIG. 8 being a diagrammatical plan view and FIG. 9 a section view taken on the line IVIV in FIG. 8.
FIG. 10 is a sectional view similar to that of FIG. 4, but turned through in the plane of the drawing.
FIG. 11 shows schematically an embodiment comprising an electro-magnet, the energizing current of which is controllable.
FIG. 12 is a diagrammatic view of a control member suitable for use in the arrangement according to FIG. 11.
FIG. 13 is a partial view of a laminated electromagnet particularly suitable for use in the arrangement of FIG. 11.
Referring to FIG. 1 the stationary guide of a guiding system is designated by 1 having a body 3 adapted to move relatively thereto. The relatively movable parts have opposite guide surfaces and 7 which are, of course, preferably flat. The body 3, which may be the tool holder of a machine tool is given translational movement by known means and, is provided with a number of channels 11, communicating with a supply of a gas 9, for example, compressed air. Through these channels 11, which open out in the guide surface 7, an air stream can be maintained between the guide surfaces 5 and 7; this stream can escape in the direction of the arrows 15 and 17. The arrangement is such that the guide surfaces are separated from each other by a hydrostatic gas cushion (the air cushion is not generated by relative movement of the bodies) and that the body 3 bears on said gas cushion in which a practical value of the thickness of the cushion may be about microns.
With this kind of guiding system the weight of the body 3 which may, if necessary, be provided with an additional weight, is chosen such that the thickness of the gas cushion remains constant with expected variations in the value of the tool force P. In this case the greater the biasing force the more constant will be the air cushion thickness with respect to the variation AP of the tool force P. In practice the gas cushion may be prestressed by a mass of 100 kgs. in order to keep the thickness of the gas cushion substantially constant with a variation of 1 kg. as noted above. In practice, the body 3 must be provided with a heavy weight giving rise to the above noted disadvantages.
By deriving the required bias force from magnets, arranged in at least one of the relatively movable parts, it is possible to obtain a force of the desired value without great increases of weight. As seen in FIG. 2, a body 23 is provided with gas ducts in the known manner and according to the invention if made from non-magnetic material, and provided with a plurality of magnets 25. The guide 27 is made from ferromagnetic material. The magnets supply the magnetic force between the opposite guide surfaces to draw the bodies towards each other. By a suitable choice of the type and the number of magnets which may, of course, also be arranged in the guide 27, it is possible to bias the gas cushion between the guide surfaces in the required or desired manner. The magnets, which may be permanent magnets or electromagnets, have a structure providing great magnetic force between the guide surfaces. Since the structure of such magnets are well known, it will not be described herein in detail.
It has been found that rapid vibrations produced in the body 23 can be substantially completely damped by the eddy currents induced by the magnets.
Since in this case the bias force is derived from magnets the invention may be carried out successfully in cases in which the guide surfaces are not horizontal. Irrespective of the positions of the guide surfaces the magnets can exert the required biasing forces on the gas cushion.
The invention is particularly suitable for guiding a movable body along an accurately fixed path. An example of such a guide is shown in FIGS. 3 and 4. It comprises a guide path 31 of ferromagnetic material and a body 33, adapted to reciprocate along said path. The body 33, the length of which is small with respect to the length of the guide path 31 viewed in the direction of displacement, is made of non-magnetic material and contains magnets 35 and 37 and a number of ducts opening out towards the guide path 31. Said ducts communicating in any known or suitable manner with a compressed-air supply. The body 33 has two guide surfaces 41 and 43, arranged at a given angle to each other, said surfaces cooperating with fixed guide surfaces 45 and 47, arranged at this same angle to each other. Between the surfaces 41 and 45 and between the surfaces 43 and 47 there is provided a biassed air cushion. Thus, a rectilinear guide is obtained, which in contrast to the known dovetail guides for precision guiding requires only two guide surfaces arranged at an angle to each other. The magnets hold the body 33 in place and in its path while the air cushion between the two sets of guide surfaces is maintained under a suitable biasing force. Said path is in this case rectilinear, but it may also be curved as illustrated in FIG. 5.
The rectilinear guide shown in FIGS. 3 and 4 can be manufactured in a particularly simple manner (see FIGS. 6 and 7). To this end a body 53, ground to flatness on one side and provided with magnets 51, 52 is held by magnetic agency to a block 55 of ferromagnetic material, also ground appropriately. The surfaces 57 and 59 are then ground to flatness in a single operation, in which it is not necessary to take special measures to provide that the angle a (FIG. 7) should be 90. A part 61 is secured to the block 55, which part is also ground on its upper or guiding side.
FIGS. 8 and 9 show a rectilinear guide, in which the guide path is formed by two stationary angular parts 63 and 65, which together guide an elongated sledge 67. Each of the parts or guides 63 and 65 are provided with magnets 68 and 69 (FIG. 9) and with ducts for the compressed air supply in the direction of the broken arrows 71. The sledge 67 is made of ferromagnetic material. The sledge 67 is not consequently provided with magnets.
With the guiding device shown in FIGS. 3 and 4, the angular guide path 31 forms, partly at least, the lower stationary part of a guiding device. This arrangement may be inverted, however, so that the position seen of FIG. 10 is obtained. The body 33 tends to fall out of the guide path 31 in this position owing to its natural Weight, but the magnets in the body 33 overcome this and in addition furnish the force required for biasing the gas cushion between the guide surfaces.
With the structures shown in FIGS. 2, 3, 4, 5, 8, 9 and 10 the magnets and the ducts opening out towards the guide surfaces are preferably arranged in the smaller of the cooperating guide elements, since this ensures very stable guiding. If the magnets are arranged in the larger of the cooperating guide surfaces, a reasonable stability could only be obtained by providing the guide path with a larger number of equidistant magnets having identical magnetic properties, which can be realized in practice only with difficulty. However, in some other arrangements such as a fixed sleeve and rotatable shaft arrangement (drill press) such an arrangement is practical.
In order to obtain a gas cushion of constant thickness use may be made, as stated above, of magnets providing a bias force which is high as compared with variations of the external load P. By employing electro-magnets it is possible to reduced the total biasing force with the same range of variations in the external load. Thus, in the case of a variation AP of the load of, for example, a chisel, the thickness d of the gas cushion will tend to diminish. By measuring or sensing slight variations in thickness of the gas cushion and by controlling the current energizing the electro-magnets, the thickness of the gas cushion can be kept constant. Such an arrangement is shown diagrammatically in FIGS. 11 and 12 in which a body 77, having an electro-magnet is movable relative to a fixed surface guide 79. A control member such as illustrated in FIG. 12 is provided for measuring the instantaneous thickness d of the air cushion, while a part of the guide surfaces operate as components of a variable capacitor. By means of the control-member 81 the measured difference in the thickness of the air cushion is converted into a variation in the energizing current of the electro-magnet 75.
A laminated electromagnet according to FIG. 13 is preferable in the arrangement according to FIG. 11. In FIG. 13 the ferromagnetic guide is indicated by 100 and a laminated electromagnet by reference numerals 101 and 102. The parts 101 being constituted of Ferroxdur material and the parts 102 are made of soft steel.
What is claimed is:
1. A system for guiding a part movable in a path relative to a supporting part comprising, a translationally movable body of relatively low mass having a substantially flat surface, a guide member having a substantially flat surface opposite the flat surface of said body for supporting said body, hydrostatic pneumatic means having openings in at least one of said surfaces for separating said body and said guide member throughout said path, and magnetic means urging said flat surfaces of said body and said guide member toward each other throughout said path for maintaining a given spaced relation therebetween, said given spaced relation being substantially equal to a similar space relation by a similar body having a significantly greater mass than the said body of low mass; said magnetic means comprising a composite body of soft steel portions separated by portions of ferromagnetic material.
2. A system according to claim 1 wherein the ratio of soft steel to ferromagnetic material is 1:2 respectively.
3. A system according to claim 1 with the addition of capacitor means for measuring the said spaced relation, and a capacitor bridge means and associated circuit means coupled with said capacitor means and said magnetic means for varying the magnetic force of said magnetic means.
4. A system for guiding a part movable in a path relative to a supporting part comprising, a translationally movable body of relatively low mass having a substantially flat surface, a guide member having a substantially flat surface opposite the flat surface of said body for supporting said body, hydrostatic pneumatic means having openings in at least one of said surfaces for separating said body and said guide member throughout said path, and magnetic means urging said fiat surfaces of said body and said guide member toward each other throughout said path for maintaining a given spaced relation therebetween, said given spaced relation being substantially equal to a similar space relation by a similar body having a significantly greater mass than. the said body of low mass.
5. A system according to claim 4 wherein said magnetic means comprises at least one electromagnet, means for measuring the said spaced relation, means for energizing said electromagnet and means coupled with said energizing means and said measuring means for varying the magnetic force of said electromagnet proportional to variations of said space.
6. A system according to claim 4 wherein said magnetic means comprises at least one permanent magnet secured in said movable body adjacent the supporting surface of said guide member and said pneumatic means is operatively connected with said body including duct means opening between said body and said supporting surface and closely adjacent said magnetic means.
7. A system for guiding a part movable in a fixed path relative to a supporting part comprising a translationally movable body of relatively low mass, a guide member for supporting said body, said guide member having a pair of angularly related guiding surfaces and said body having a corresponding angularly related pair of surfaces adjacent said pair of guiding surfaces, hydrostatic pneumatic means having openings in at least one of said surfaces for maintaining said body and guide member in spaced relation, and magnetic means for biasing said body and said guide member toward each other to maintain said spaced relation substantially equal to a similar space relation determined by another body having a significantly greater mass than said body of low mass.
8. A system according to claim 7 wherein said magnetic means comprises at least one electromagnet, means for measuring the said space relation, means for energizing said electromagnet and means coupled with said energizing means and said measuring means for varying the magnetic force of said electromagnet proportioned to variations of said space.
9. A system according to claim 7 wherein said magnetic means comprises at least one electromagnet in said body flush with each said angularly related surface and said pneumatic means is operatively connected with said body including duct means opening at each said angularly related surface for supporting said body on Said guide member.
References Cited by the Examiner UNITED STATES PATENTS 2,942,385 6/1960 Pal.
FOREIGN PATENTS 1,046,637 12/1958 Germany.
OTHER REFERENCES Air Lubricated Bearing: published in the 1953 Annual Handbook of Product Engineering. Pages J2 through J5 relied upon.
DAVID J. WILLIAMOWSKY, Primary Examiner. FRANK SUSKO, Examiner.