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Patent US5680795 - Mechanical drive assembly incorporating counter-spring biassed radially ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsAn anti-friction nut for engagement with an elongate shaft-like member having a groove with opposed walls. The nut body has an axial bore which is adapted to receive the shaft-like member, and a radial bore communicating with the axial bore. The radial bore carries an anti-friction roller mounted by...http://www.google.com/patents/US5680795?utm_source=gb-gplus-sharePatent US5680795 - Mechanical drive assembly incorporating counter-spring biassed radially-adjustable rollersAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS5680795 APublication typeGrantApplication numberUS 08/498,358Publication dateOct 28, 1997Filing dateJul 5, 1995Priority dateJul 5, 1995Fee statusPaidAlso published asUS5860324, WO1997002441A1Publication number08498358, 498358, US 5680795 A, US 5680795A, US-A-5680795, US5680795 A, US5680795AInventorsJohn D. ParsonsOriginal AssigneeNorco Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (18), Referenced by (8), Classifications (9), Legal Events (17) External Links: USPTO, USPTO Assignment, EspacenetMechanical drive assembly incorporating counter-spring biassed radially-adjustable rollers
US 5680795 AAbstract
An anti-friction nut for engagement with an elongate shaft-like member having a groove with opposed walls. The nut body has an axial bore which is adapted to receive the shaft-like member, and a radial bore communicating with the axial bore. The radial bore carries an anti-friction roller mounted by means of two back-to-back ball bearing assemblages. A nose portion of the roller extends into the axial bore and engages one wall of the groove of the shaft-like member. There is a spring in the radial bore which engages the outer race of the inner ball bearing assemblage, and effectively biases the roller in a radially outward direction, away from the shaft-like member. A threaded adjustment plug in the bore engages the outer race of the outer-most ball bearing assemblage, to effect adjustable movement of the roller in radial directions, against the action of the spring. Reduced looseness and backlash are realized.
1. An anti-friction nut for engagement with an elongate shaft-like member having a groove with opposed walls, said nut comprising in combination:a) a nut body having an axial bore which is adapted to receive the elongate shaft-like member, b) said nut body having a radial bore communicating with the axial bore thereof, c) an anti-friction roller having at one end a nose portion, d) mounting means including an anti-friction bearing, turnably mounting the roller in the radial bore such that the nose portion of the roller extends into said axial bore and engages one wall of the groove of said elongate shaft-like member, e) a spring carried in the radial bore of the nut body, said spring engaging said bearing and biasing the roller in a radially outward direction away from said elongate shaft-like member, and f) adjustment means carried by the nut body in said radial bore and disposed radially outwardly of said bearing, said adjustment means being operable to effect adjustable movement of the roller in radial directions, g) the engagement of said spring with the bearing acting to bias the latter radially outward against said adjustment means so as to take up any looseness of the bearing, h) said radial bore of the nut body having a portion containing internal threads, i) said adjustment means comprising an externally threaded plug carried in the radial bore, and the threads of the plug mating with the internal threads of the said radial bore, whereby turning of the plug effects radial movement of the anti-friction roller. 2. An anti-friction nut as claimed in claim 1, wherein:a) said spring, in biasing said mounting means against said adjustment means, imparts a frictional drag between the said mating threads of the plug and bore, and thus inhibits inadvertent turning or loosening of the plug under conditions of operation or vibration. 3. An anti-friction nut for engagement with an elongate shaft-like member having a groove with opposed walls, said nut comprising in combination:a) a nut body having an axial bore which is adapted to receive the elongate shaft-like member, b) said nut body having a radial bore communicating with the axial bore thereof, c) an anti-friction roller having at one end a nose portion, d) mounting means including an anti-friction bearing, turnably mounting the roller in the radial bore such that the nose portion of the roller extends into said axial bore and engages one wall of the groove of said elongate shaft-like member, e) a spring carried in the radial bore of the nut body, said spring engaging said bearing and biasing the roller in a radially outward direction away from said elongate shaft-like member, and f) adjustment means carried by the nut body in said radial bore and disposed radially outwardly of said bearing, said adjustment means being operable to effect adjustable movement of the roller in radial directions, g) the engagement of said spring with the bearing acting to bias the latter radially outward against said adjustment means so as to take up any looseness of the bearing, h) said anti-friction bearing comprising two end-to-end ball bearing assemblages, each ball bearing assemblage having an inner race that is rigid with the roller, and each ball bearing assemblage having an outer race that slidably engages the wall of the radial bore, i) said spring acting on the outer races of said end-to-end ball bearing assemblages so as to bias the assemblages and the roller radially outwardly, j) said adjustment means comprising an externally threaded plug carried in the radial bore, said plug having an annular shoulder at its inner end, the annular shoulder being engaged solely by the outer race of one ball bearing assemblage. 4. An anti-friction nut as claimed in claim 3, and further including an adhesive material applied between the inner races of the ball bearing assemblages and the roller, to substantially rigidly secure both inner races to the roller.
5. An anti-friction nut for engagement with an elongate shaft-like member having a groove with opposed walls, said nut comprising in combination:a) a nut body having an axial bore which is adapted to receive the elongate shaft-like member, b) said nut body having a radial bore communicating with the axial bore thereof, c) an anti-friction roller having at one end a nose portion, d) mounting means including an anti-friction bearing, turnably mounting the roller in the radial bore such that the nose portion of the roller extends into said axial bore and engages one wall of the groove of said elongate shaft-like member, e) a spring carried in the radial bore of the nut body, said spring engaging said bearing and biasing the roller in a radially outward direction away from said elongate shaft-like member, and f) adjustment means carried by the nut body in said radial bore and disposed radially outwardly of said bearing, said adjustment means being operable to effect adjustable movement of the roller in radial directions, g) the engagement of said spring with the bearing acting to bias the latter radially outward against said adjustment means so as to take up any looseness of the bearing, h) said anti-friction bearing comprising two end-to-end ball bearing assemblages, each ball bearing assemblage having an inner race that is rigid with the roller, and each ball bearing assemblage having an outer race that slidably engages the wall of the radial bore, i) said spring acting solely on the outer race of one ball bearing assemblage so as to bias it and the roller radially outwardly, j) the radial bore of the nut body having an inner shoulder adjacent its axial bore, k) said shoulder being engaged by and constituting a seat for said spring. 6. An anti-friction nut as claimed in claim 5, wherein:a) said spring comprises a pair of back-to-back bowed spring washers, each washer having a peripheral edge portion, b) the peripheral edge portion of one of the spring washers engaging said inner shoulder of the radial bore. 7. An anti-friction nut as claimed in claim 5, wherein:a) said spring comprises a pair of back-to-back bowed spring washers, each spring washer having a peripheral edge portion, b) the peripheral edge portion of one of the washers engaging the outer race of one ball bearing assemblage. 8. An anti-friction nut as claimed in claim 5, wherein:a) said spring comprises two pairs of back-to-back bowed spring washers, each washer having a peripheral edge portion, b) the peripheral edge portion of one of the washers engaging said inner shoulder of the radial bore, c) the peripheral edge portion of another of the washers engaging the outer race of one ball bearing assemblage. 9. An anti-friction nut as claimed in claim 8, wherein:a) the holes in each said spring washer are substantially axially aligned with one another, and b) the roller extending through said axially aligned holes. 10. An anti-friction nut as claimed in claim 9, wherein:a) said roller comprises an elongate shank of smaller dimension than that of the nose portion, b) said shank having an annular shoulder at the nose portion, c) said annular shoulder abuttingly engaging the inner race of one ball bearing assemblage. Description
1. My co-pending application U.S. Ser. No. 08/333,735, filed Nov. 3, 1994, entitled "MECHANICAL OSCILLATOR", and having common ownership with the present application.
This invention relates to reciprocating drive mechanisms, and more particularly to devices of the type incorporating one or more anti-friction rollers that are turnably mounted in a nut body and which extend into the axial bore of the body so as to engage the walls of a grooved or threaded shaft, such as a screw or other shaft having a roller-receiving groove.
The entire disclosure of U.S. application Ser. No. 08/333,735 above identified is specifically incorporated by reference, into the present application.
The listing of prior art set forth in the above identified application is re-produced hereinbelow:
______________________________________U.S. Pat. Nos.:______________________________________3,296,880      3,308,674    3,766,7883,766,800      3,779,094    4,008,6254,022,076      4,031,765    4,198,8724,199,999      4,343,200    5,191,805______________________________________ British Patent No. 1044 dated Jan. 15, 1907 French Patent No. 526,586
The present invention relates to improvements in the constructions illustrated and described in U.S. Pat. No. 3,792,616 dated Feb. 19, 1974, and U.S. Pat. No. 5,191,805 dated Mar. 9, 1993.
U.S. Pat. No. 5,191,805 describes an especially simple, miniature low-friction mechanical transmission incorporating a threaded shaft and a cooperable nut adapted to be reciprocated thereon in response to turning of the shaft. In the disclosed construction, the nut is provided with a radial bore that houses two back-to-back ball bearing assemblages and a roller having an enlarged, conical nose portion which extends into the axial bore of the nut body, for engagement with the thread grooves.
The roller is secured to the inner races of each ball bearing assemblage by means of an adhesive, such that the roller and inner races become rigid with one another, and turn as a unit. The outer races of each ball bearing assemblage are similarly secured in place in the bore, at the desired, adjusted radial position, by an adhesive. When the adhesive has dried, the roller occupies a generally fixed radial position in the radial bore, and turns as a consequence of the engagement of its conical nose with the wall surfaces of the thread groove.
This patented construction has the advantage of extreme simplicity, whereby the number of separate components is kept to an absolute minimum. In addition, the use of adhesive for securing the parts together has been found to be surprisingly cost-effective, even in view of the need for some limited manual assembly of the parts.
In spite of the success of the patented structure, there still exists a need to economize from the standpoint of utilizing components which can be standardized to an extent, so as to permit off-the-shelf selection as to screw length, diameter, pitch, and thread resolution.
While the patented construction was deemed to be acceptable for many applications, it was considered that enhanced flexibility could be attained if it were possible to provide a simple and effective means for imparting fine or incremental adjustability to the radially disposed rollers, in applications where looseness was not tolerable, or where special speed and load conditions prevailed.
The earlier U.S. Pat. No. 3,792,616, relates to a mechanical oscillator or reciprocating drive which employs two roller cartridges that are respectively received in axially spaced radial bores of a nut body. The shaft has two spaced-apart endless grooves that are substantially duplications of one another. The spacing of the rollers on the nut body is such that one roller engages a wall of one groove, and the other roller engages the similarly-facing wall of the second groove. An objective of this construction was to achieve a balance between the load on each roller. As shown in FIG. 3 of the patent, the rollers each had at their radially outermost ends, spring washers which, acting through a ball bearing, biased the respective roller in a radially inward direction. Upon experiencing load, the conical configuration of the roller nose gave rise to a tendency for the roller to retract in a controlled manner, against the action of the springs. The disclosed device has enjoyed considerable success in the commercial and industrial market, since the issuance of the patent.
As in the previous U.S. patent noted above, No. '805, there was no provision in the '616 patent for fine or micro-adjustment in the radial position of the roller. In practice, the rollers were fixed in their respective roller cartridges at a position determined by the stiffness of the springs and the pressure exerted on the roller by the wall of the groove of the shaft. It was assumed that the tolerances on the various components were sufficiently close that the desired, balanced drive condition would automatically be established at the time that the unit was first entered into service.
In practice, this was not always the case, however, and attempts to improve on the patented constructions are continuously being made.
The above disadvantages and drawbacks of prior anti-friction drive assemblies are largely obviated by the present invention, which has for an object the provision of a novel and improved anti-friction nut and grooved shaft, which are simple in structure, and rugged and reliable in operation over extended periods of use.
A related object of the invention is to provide an improved anti-friction nut and grooved shaft as above set forth, which are especially adapted for high-speed operation, with a minimum of sliding or scraping of the rollers on the walls of the groove of the shaft.
Still another object of the invention is to provide an improved anti-friction nut and grooved shaft of the kind indicated, wherein the disposition of the rollers is such that they can be made essentially unidirectional in their turning movements, thereby avoiding potential problems resulting from inertia of the rollers and the inability of the rollers to turn first in one direction, suddenly halt, and thereafter turn rapidly in the opposite direction.
Yet another object of the invention is to provide an improved anti-friction nut and grooved shaft as above characterized, wherein an especially simple and relatively high-resolution adjustment of the radial position of the rollers is had, all to the end that there is minimized excessive looseness between the parts, and with no appreciable added drag on the rollers occurring as a consequence of the adjustability feature.
Still another object of the invention is to provide anti-friction nut constructions in accordance with the foregoing, which lend themselves to use with shafts that are characterized by either conventional spiral thread grooves, or single-loop type, endless grooves.
Economy of manufacture and assembly, coupled with minimal wear and convenient adjustability are thus realized, in a device utilizing relatively few components than be conveniently fabricated from steel, bronze, and molded plastic.
In accomplishing the above objects the invention provides an anti-friction nut for engagement with an elongate screw or shaft-like member having a groove with opposed walls, the nut comprising in combination a nut body having an axial bore which is adapted to receive the shaft-like member, and having a radial bore communicating with the axial bore thereof. There is an anti-friction roller having at one end a nose portion, and mounting means are provided, including an anti-friction bearing, turnably mounting the roller in the radial bore such that the nose portion of the roller extends into the axial bore and engages one wall of the groove of the shaft-like member. There is a spring carried in the radial bore of the nut body and engaging the bearing, so as to bias the roller in a radially outward direction away from the shaft-like member. Adjustment means are also provided, disposed in the radial bore of the nut body and positioned radially outwardly of the bearing, to effect adjustable movement of the roller in a radial direction. The spring normally biases the mounting means radially outward and against the adjustment means so as to take up any looseness of the parts.
The invention also provides a mechanical cam drive assembly, comprising in combination a first member having a spiral groove with opposed walls and characterized by a predetermined pitch measured along an axis thereof, and a second member comprising a nut body cooperable with the first member. The nut body has radial bores and a plurality of anti-friction rollers turnably mounted therein, respectively. The rollers each have a nose portion which projects from its respective radial bore, and which engages the walls of the groove of the first member. The rollers are spaced apart axially along the first member, by a distance which is a micro-fraction larger than the pitch of the groove of the first member.
The invention further provides a mechanical cam drive assembly, comprising in combination a first member having two grooves each with opposed walls, and a second member comprising a nut body cooperable with the first member. The nut body has radial bores which carry a plurality of anti-friction rollers respectively, the rollers each having at one end a nose portion which projects from its radial bore. The nose portions are engageable with walls of the grooves of the first member. The rollers are spaced apart about the first member such that one roller continuously engages one wall of one of the grooves, and another roller continuously engages an oppositely-facing wall of the other of the grooves.
The arrangement is such that each roller can, at all times, be positively backed up and rigidly engaged by the adjustment means associated with it, and thus cannot move radially outward from an intermediate position in its radial bore, even in the presence of a momentary high load.
Setting of the adjustment means is accomplished manually, in such a manner as to either reduce backlash, or alternately equalize the load on two or more rollers.
FIG. 1 is a front view, partly in elevation and partly in axial section, of a mechanical drive assembly comprising an anti-friction nut carried on a screw.
FIG. 2 is a view like FIG. 1, of a modified mechanical drive assembly, constituting another embodiment of the invention.
FIG. 3 is a fragmentary axial section of the nut body of the drive assembly of FIG. 1.
FIG. 4 is a diagrammatic representation of the screw portion of the mechanical drive assembly of FIG. 2, and illustrating anti-friction rollers of the nut, and wherein the roller spacing measured axially of the screw is substantially the same as the pitch or lead of the screw.
FIG. 5 is a diagrammatic representation of the screw portion of the mechanical drive assembly of FIG. 2, and illustrating anti-friction rollers of the nut, and wherein the roller spacing measured axially of the screw is a micro-fraction greater than the pitch or lead of the screw, constituting another embodiment of the invention.
FIG. 6 is a front view, partly in elevation and partly in axial section, of a reciprocating mechanical drive assembly comprising a shaft having two endless grooves spaced from one another, and comprising an anti-friction nut carried on the shaft, constituting yet another embodiment of the invention.
FIG. 7 is a front elevation of the shaft per se, of FIG. 6.
FIG. 8 is diagrammatic representation of the shaft of FIGS. 6 and 7, illustrating anti-friction rollers carried by the nut of FIG. 6, and wherein the roller spacing measured axially of the shaft approximates the axial spacing between the endless grooves thereof.
FIG. 9 is a diagrammatic representation of the shaft of FIGS. 6 and 7, illustrating anti-friction rollers carried by the nut of FIG. 6, and wherein the roller spacing measured axially of the shaft is a micro-fraction greater than the axial spacing between the endless grooves thereof.
FIG. 10 is a vertical section of a threaded adjustment plug utilized in the anti-friction nuts of the mechanical drive assemblies of FIGS. 1 and 3; FIG. 2; and FIG. 6, respectively, and
FIG. 11 is a vertical section of a modified threaded plug, having projecting prongs to facilitate its adjustment, and showing a chisel being applied to the prongs following adjustment, so as to shear them off and render the plug tamper-resistant.
Referring first to FIG. 1, there is illustrated a mechanical drive assembly which is generally designated by the numeral 10, comprising a first member in the form of a shaft or screw 12 having a spiral thread groove 14, and a second member comprising an anti-friction nut 16. The latter includes an elongate nut body 18 shown in FIG. 3, which has an axial bore 20 to receive the screw 12. Preferably, end bearings in the form of bronze sleeves 21 are provided, disposed in annular recesses of the nut body 18.
The nut body 18 is adapted to traverse the screw 12 when the latter is turnably driven by suitable powered means (not shown). The groove 14 in the screw 12 has opposed, facing walls 22 and 24, and a bottom wall 26.
The nut body 18 (FIG. 3) is provided with an anti-friction groove-engagement means 27, adapted to be carried in a radial bore 28 which extends into and communicates with the axial bore 20 thereof. The anti-friction groove-engagement means 27 is turnably mounted in the radial bore 28 and comprises a roller 30 which is mounted in anti-friction bearings, the latter preferably taking the form of back-to-back ball bearing assemblages 32 and 34. The roller 30 comprises an elongate shank portion 36, and at its inner end, a nose portion 38. The shank portion 36 is of reduced diameter with respect to the nose portion 38, and the two portions meet at an annular shoulder 40. The nose portion 38 is adapted to extend into the axial bore 20 of the nut body 18, for engagement with one or the other of the walls 22, 24 of the spiral groove 14 of the screw. The nose portion is, however, spaced a finite distance from the bottom of the groove, so as to avoid contact therewith and possible scraping thereagainst.
In accordance with the present invention, the anti-friction groove-engagement means 27 comprising the roller 30, not only provides an especially simple overall mounting structure, but also permits an unusually quick and easy manual adjustment of the radial position of the roller 30 to be had with a remarkably high degree of resolution and precision. In accomplishing this improved mounting, there are provided in combination with the ball bearing assemblages 32 and 34, an adjustment means and a resilient spring means, the latter biasing and positioning the roller 30 in a radially outward direction, and comprising resilient bowed spring washers 42; the adjustment means comprises a threaded adjustment plug 44 that is carried in the bore 28 and disposed radially outwardly of the roller 30.
By the invention, the radial bore 28 has an inner shoulder 46 adjacent to the axial bore 20 of the nut body, constituting a seat for the spring washers 42. In a preferred embodiment, multiple spring washers 42 are utilized in back-to-back relation, typically two or four in number. In FIG. 3, one of the spring washers 42 occupies the seat formed by the shoulder 46. Countering the force of the washers 42 is the threaded adjustment plug 44. The radially outermost portion of the bore 28 is internally threaded as shown, and the mating external threads of the plug 44 enable its radial position to be manually adjusted as needed, utilizing a suitable tool or instrument (not shown). In the form shown, the plug 44 has two off-center keying holes 48 into which the tines of such an instrument are inserted, during the adjustment.
Also, in accordance with the invention the mounting arrangement for the roller 30 is such that neither the shank 36 nor the nose portion 38 thereof is directly engaged by either the spring washers 42 or the threaded adjustment plug 44. As shown in FIG. 3, where four spring washers 42 are utilized, the periphery of the radially innermost spring washer engages the shoulder 46 of the nut body. The periphery of the radially outermost spring washer 42 engages solely the outer race of the inner ball bearing assemblage 34, with the holes in the spring washers 42 being sufficiently large so as to completely clear the enlarged nose portion 38 of the roller 30.
Similarly, the inner end of the threaded adjustment plug 44 is provided with an annular shoulder 50 defining a clearance recess 52. The shoulder 50 is dimensioned to engage solely the outer race of the radially outermost ball bearing assemblage 32, as shown. Thus, the roller 30 per se engages solely the inner races of the ball bearing assemblages 32, 34, and no interference with free turning is encountered by the roller 30, either from the plug 44 or the spring washers 42.
In the preferred embodiment, the roller 30 can be permanently and rigidly secured to the inner races of the ball bearing assemblages 32, 34 by suitable adhesive, such as that manufactured under the trademark LOCTITE brand adhesive. Under such circumstances, the radially innermost ball bearing assemblage 34 is positioned with its inner race firmly against the shoulder 40, and the radially outermost ball bearing assemblage 32 abuts the inner ball bearing assemblage 34. The outer races of each ball bearing assemblage are of a dimension to allow a free-sliding fit with the walls of the radial bore 28 of the nut body 18, such that the two ball bearing assemblages 32, 34 and secured roller 30 move radially in the bore 28, as a unitary assembly.
The spring washers 42 thus operate to bias the radially outermost ball bearing assemblage 32 into continuous engagement with the annular shoulder 50 of the threaded adjustment plug 44; as the latter is turned, the roller 30 and ball bearing assemblages 32, 34 move as a unit, either radially inwardly or outwardly, the spring washers 42 maintaining an essentially continuous contact and engagement between the radially outermost bearing assemblage's outer race and the threaded adjustment plug 44. The adjustment plug 44 thus can vary the radial position of the roller 30 with respect to the nut body 18, simultaneously compressing the spring washers 42 by a greater or lesser amount depending on the direction of turning of the plug 44.
Another embodiment of the invention is illustrated in FIGS. 2 and 5, wherein advantage is taken of the roller adjustment to eliminate lost motion in a screw drive device of the kind described above. In this embodiment, two roller assemblages are arranged in tandem in a multi-cavity nut body having two radial bores extending into a single axial screw-accommodating bore. As shown, there is provided on the screw 12, the nut body 54 having radial bores 56 and 58 which merge into a common axial bore 60. The nut body 54 carries first and second anti-friction groove-engagement means 62 and 64, respectively which are identical to the anti-friction groove-engagement means 27 described above in connection with FIGS. 1 and 3. The axial spacing between the first and second radial bores 56 and 58 respectively can be chosen to be equal to a multiple of the pitch of the thread groove 14 plus or minus a small micro-fraction of the pitch, as will be explained hereinbelow.
The roller 66 of the groove-engagement means 62 is identical to roller 30, having an elongate shank portion and a nose portion which extends into the axial bore 60, the two portions meeting at an annular shoulder. The roller 68 of the second groove-engagement means 64 also has a nose portion which extends into the axial bore 60 of the nut body 54. The nose portions are arranged for selective engagement with walls 22, 24 of the spiral groove 14 of the screw.
The mounting arrangements for rollers 66 and 68 are substantially the same as that described above in connection with roller 30. First and second spring means respectively bias the rollers 66 and 68 in radially outward directions, and adjustment means comprising first and second adjustment plugs 70, 72 are carried in the bores 56, 58 respectively and disposed radially outwardly of the rollers 66, 68. Each radial bore has an inner shoulder adjacent to the nut body's axial bore 60. Such shoulders are similar to that indicated 46 in FIG. 3, and each constitutes a seat for the respective spring means. As with the roller 30, the spring means for each of the rollers 66, 68 preferably comprises either two or four back-to-back resilient spring washers. Countering the force of the spring means are the plugs 70, 72. The radially outermost portions of the bores 56, 58 are internally threaded as shown, to accommodate the plugs 70, 72.
The first and second plugs 70, 72 can optionally have one or more offset key holes similar to those indicated 48 in FIG. 3, which can accept the tines (not shown) of an adjustment tool during adjustment of the rollers 66, 68 respectively.
As previously noted in connection with the embodiment of FIGS. 1 and 3, in the case of the embodiment of FIG. 2, neither the shank nor the nose portion of either roller 66, 68 is directly engaged by the respective spring washers (corresponding to spring washers 42 in FIG. 3) or by the adjustment plugs 70, 72. Where four back-to-back spring washers are used in each bore 56, 58, the innermost spring washer engages the respective shoulder (corresponding to shoulder 46 of FIG. 3), whereas the outermost washer engages solely the outer race of the radially innermost ball bearing assemblage (corresponding to ball bearing assemblage 34 in FIG. 3). The peripheries of the spring washers surround but do not contact the enlarged nose portions respectively, of the rollers 66, 68, the holes in the spring washers instead being sufficiently large to effect such clearance.
In addition, each adjustment plug 70, 72 has an annular shoulder which engages solely the outer race of the radially outermost ball bearing assemblage (corresponding to ball bearing assemblage 32 in FIG. 3), as shown. Again, there occurs no impediment to free turning of either roller 66 or 68, from the plugs 70, 72 or from the spring washers.
The roller 66 is permanently and rigidly secured to both inner races of its ball bearing assemblages by suitable adhesive, such as that manufactured under the trademark LOCTITE brand adhesive. The radially innermost ball bearing assemblage is positioned with its inner race firmly against the shoulder of the roller 66, and the radially outermost ball bearing assemblage abuts the radially innermost ball bearing assemblage. The outer races of each ball bearing assemblage are of a dimension to allow a free-sliding fit with the walls of the radial bore 56, such that the two ball bearing assemblages and secured roller 66 move radially in the bore, as a unitary assembly.
A similar arrangement is provided for roller 68, with respect to its ball bearing assemblages.
In the case of roller 66, the spring washers thus operate to bias its radially outermost ball bearing assemblage into continuous engagement with the annular shoulder of the adjustment plug 70; as the latter is turned, the assembly of roller 66 and ball bearing assemblages moves radially inwardly or outwardly, the spring washers maintaining the essentially continuous contact and engagement between the outer race of the radially outermost ball bearing assemblage and the threaded plug 70. The threaded plug 70 thus varies the radial position of the roller 66 with respect to the nut body 54, and simultaneously compresses the spring washers by a greater or lesser amount, depending on the direction of turning of the plug 70.
The same is true of the threaded plug 72 and the roller 68.
The disclosed arrangement involving two rollers 66, 68 turnably carried respectively in two, axially spaced radial bores 56, 58 can be advantageously utilized to provide either a substantially increased load capability for the nut body 54 and screw 12, or a reduced backlash feature, depending upon the disposition of the one radial bore 56 with respect to the other radial bore 58.
In the case where the axial spacing between the radial bores 56, 58 is equal to the pitch of the groove 14 in the screw 12 plus a micro-fraction thereof; or alternately, is equal to a multiple of such pitch plus a micro-fraction thereof, the resulting spacing of the rollers 66, 68 will be such as to cause one roller 66 to engage one wall 22 of the groove 14, while the other roller 68 engages the oppositely-directed wall 24 of the groove 14, as diagrammatically illustrated in FIG. 5. This has the advantage of reducing backlash between the nut body 54 and screw 12, in that for relatively light loads, one roller 66 carries substantially the entire load when the nut body 54 is traversing the screw 12 in one axial direction, with the other roller 68 carrying substantially the entire load when the nut body 54 is traversing the screw 12 in the opposite axial direction. At the points where the axial direction of the load reverses, the lost motion, constituting backlash, can be considerably reduced over that obtainable with a single roller. In effect, the engagement of the rollers with their respective, opposed groove walls tends to maintain the nut body in a defined central position, in an axial sense with respect to the axis of the screw. This construction is in contrast to that where a single roller is employed, and where the roller must shift, at a point of load reversal, from engagement with one groove wall, for example wall 22, to the opposite groove wall, for example wall 24, the shift giving rise to excessive looseness or backlash.
On the other hand, if low backlash is not the primary concern, the radial bores 56, 58 in the nut body 54 can be spaced axially by a distance which is substantially equal to the groove pitch or a multiple thereof, with no correction or deviation. Such a condition is diagrammatically illustrated in FIG. 4, wherein by suitable adjustment of the threaded plugs 70 and 72, the rollers 66, 68 can be set to substantially equally share the load. In practice, there does not occur a truly equal division of load between the rollers 66, 68 in FIGS. 2 and 4, because of imperfections in the screw as it is traversed along its length, and also variations in groove concentricity, as from less than ideal manufacturing tolerances. Typically, the screws are produced in a conventional screw machine, and with time, the components of the machine suffer wear, which in turn compromises uniformity in their thread/groove formations in the screws produced thereby.
It is noted that with the present invention, each roller 66, 68 occupies an intermediate radial position in its respective radial bore 56, 58. The exact positions are determined by manual adjustment of the respective threaded plugs 70, 72, typically in alternating fashion, against the counterforces of the spring washers (corresponding to spring washers 42 of FIG. 2).
It is further noted that with the disclosed arrangement, in each case the threaded plugs 70, 72 positively back up and support the respective rollers 66, 68, through the ball bearing assemblages. This construction is in contrast to some prior constructions where anti-friction rollers were spring biased radially inwardly into engagement with the walls of a grooved shaft. With the present invention, there is virtually no radially outward yielding of either roller 66 or 68 in response to a load applied thereto, which is considered to result in improved load-handling capability between the shaft and nut body.
Further, referring again to FIG. 3 and in accordance with the invention the threaded plug 44, once set, can be rendered largely tamper-resistant by filling its keying holes 48 with a quantity 74 of suitable cement or epoxy, as in FIG. 10. Once cured, the epoxy 74 effectively prevents subsequent insertion of the adjustment tool (not shown) utilized to initially advance or retract the plug 44 toward its desired, adjusted position.
Also by the invention, a small quantity of cement is applied to the threads of the plugs 70, 72 after they have been initially set. A preferred form of cement is that sold under the Trademark LOCTITE brand adhesive which can be of the type especially formulated to readily flow around the interstices of a thread form and thereafter solidify. However, other adhesive formulations may be utilized, if desired.
An alternate tamper-resistant feature applicable to the threaded plug 44 of FIG. 3 is shown in FIG. 11, illustrating a modified plug 44a having two upstanding posts 76 by which the plug can be initially engaged and turned in its radial bore. Following adjustment and application of a cement to the threads of the plug 44a, a chisel 78 or other sharp tool is utilized to shear off the posts 76, thereby leaving a relatively smooth surface that is devoid of any remaining tool-engageable projections. In combination with the cemented threads, the lack of any such projections on the upper surface of the plug 44a effectively discourages attempts to subsequently re-adjust the plug, which is considered important from the standpoint of reliability; strictly speaking, the proper, initial adjustment is intended to be carried out at the manufacturing facility. Any attempts at re-adjustment in the field are considered best avoided. The tamper-resistant feature just described is enhanced in the case that the upper surface of the plug 44 is recessed into the bore 28 as shown in FIG. 3. The existence of the recess renders the outer surface of the plug still more difficult to access, further discouraging any subsequent attempts at re-adjustment.
Further, in accordance with the present invention the nut body 54 is preferably constituted of plastic substance, such as DELRIN (a registered trademark)brand plastic, or polycarbonate, the latter material being especially adapted for molding multiple units in mass production; in addition, in FIG. 2 the axial bore 60 of the nut body 54 is provided with spacer means in the form of slide bearings 80 preferably constituted of bronze. These bearings thus eliminate any physical contact between plastic and metal, namely the plastic body and the steel screw. This feature is considered important from the standpoint of ruggedness and long life, since sliding contact between a plastic body and a grooved or threaded shaft, would likely lead to deterioration or abrasion of the plastic. With the present construction, such a possibility is completely obviated.
In the embodiment of FIG. 2, one end of the nut body 54 is provided with an externally threaded portion, which mates with corresponding carriage plate 82 having one or more mounting holes 84, for securement of the nut body 54 to the equipment (not shown) with which the mechanical drive assembly is to be utilized. In the embodiment of FIG. 1, there are two threaded portions, and it can be understood that either or both are available for securement to equipment (not shown) by means of plates similar to that designated 82 in FIG. 2.
Yet another embodiment of the invention is illustrated in FIGS. 6, 7 and 9, wherein there is provided a reciprocating drive mechanism generally designated by the numeral 86, comprising a grooved shaft 88 and an anti-friction nut 90 comprising a nut body 92. The shaft 88 has a pair of axially spaced-apart endless grooves 94, 96, having reversing portions 98, 100 and 102, 104, respectively and spiral groove portions that are intermediate their reversing portions. The nut body 92 has an axial bore 106 fitted with sleeve bearings 108. By the invention there are provided two spaced radial bores 112, 114, and the nut body 92 carries first and second anti-friction groove-engagement means 116, 118, respectively which are identical to the anti-friction groove-engagement means 27 described above in connection with FIGS. 1 and 3, and to the anti-friction groove-engagement means 62, 64 of the embodiment of FIG. 2.
The groove engagement means 116, 118 comprises anti-friction rollers 120, 122 corresponding to the rollers 66, 68 of the embodiment of FIG. 2. As in the previous embodiments the rollers are carried on ball bearing assemblages, two bearing assemblages per roller, and spring means are included at the inner ends of the bores 112, 114, engageable with shoulders in each bore corresponding to the shoulder 46 of FIG. 3. The inner races of the ball bearing assemblages are rigid with the respective roller, as by either a press fit, or with the use of adhesive, and the outer races of the ball bearing assemblages are received in the respective radial bores with a sliding fit. Adjustment plugs similar to those of the previous embodiments are provided, disposed radially outward of the respective rollers.
By the invention, the rollers 120, 122 are mounted in substantially a single axial plane (not shown) that bisects the shaft 88 axially, and the spacing between the rollers 120 and 122, measured axially of the shaft, is just slightly greater than the axial spacing between the grooves 94 and 96, measured center to center. Each roller 120, 122 occupies an intermediate position in its bore, and the arrangement is such that by adjustment of the respective threaded plugs, one roller 120 engages the one wall 124 of the first groove 94, and the second roller 122 engages the oppositely facing wall 126 of the second groove 96, as diagrammatically depicted in FIG. 9.
The feature just described, wherein one roller always engages solely one wall of one groove, and the other always engages the oppositely facing wall of the other groove has important advantages that are not readily apparent upon a first or cursory inspection.
In particular, under high speed conditions involving a driven shaft 88 and a reciprocating nut 90, the rollers 120 and 122 are forced to turn at a significantly higher r.p.m. than the shaft 88, due to the relatively small diameters of the nose portions of the rollers. As a consequence, the inertia of the rotating rollers 120, 122 becomes significant. By the present invention, there is completely eliminated the necessity to overcome the inertia occasioned by a complete halt and subsequent (almost instantaneous) reversal of the direction of rotation of a roller, since each roller 120, 122 always rotates about its axis in the same direction, but at a speed depending upon the particular region of its own groove that is being traversed.
This arrangement is in sharp contrast to modes of operation of the devices of the prior art, wherein there occurred shifting of a roller element between one wall of a groove and the other, as required during a reversal of axial movement of a nut. The requirement of having to reverse a rotating roller abruptly, of necessity placed significant restraints on the permissible speed of operation of the device, since the friction between the individual rollers and the walls of the thread grooves was limited; if the speed were increased beyond a certain point, there arose a tendency for a roller to not reverse turning at all, but instead adopt a sliding-type movement in its groove. Sliding occurred because it was not possible to instantaneously halt the roller at the end of the groove and immediately impart a full, reverse turning movement to it as the nut reversed direction.
The present construction obviates the problems associated with roller reversal, in that each roller turns unidirectionally, for a given sense of relative turning of the shaft and nut body. Greatly increased speed is realizeable, along with increased load-carrying capability, and significantly reduced wear as occasioned by the rollers rolling against the walls of the groove instead of sliding against these walls. In preferred form, the taper of the nose portions of the rollers matches the taper of the grooves in the shaft, so as to maximize the tendency for rolling movement of a roller along a groove wall, as opposed to an undesirable sliding therealong.
A modification of the construction of FIGS. 6, 7 and 9, is indicated diagrammatically in FIG. 8. By the invention, the radial bores housing the rollers 120, 122 are disposed such that the axial spacing between the rollers is substantially equal to the axial spacing between the grooves 94, 96, measured center to center. Each roller occupies an intermediate position in its bore, and the arrangement is such that by adjustment of the plugs, both rollers 120 and 122 can be set so as to engage the similarly-directed or similarly-facing walls 124, 128, FIG. 8, of the respective grooves 94 and 96, and to share or divide the load to at least some extent. In practice, with variations in groove spacing as typically encountered in manufacturing, slight irregularities arise in the spacing between different parts of the grooves 94 and 96; the overall effect of the rollers being positioned in this manner is to smooth out any impulse-type movements which might otherwise occur with a single roller, and to provide a generally balanced drive, where the average load of each roller, over a complete reciprocation of the nut body, is generally shared with the other.
The embodiment of FIG. 8 does not enjoy the advantage noted above in connection with the embodiment of FIG. 9, in that there does occur reversal of the direction of turning of each roller, typically at the opposite ends of the grooves, the exception being where the load that is applied to the nut is always in one direction and wherein load varies between a relatively large unidirectional load to a smaller unidirectional load, as might be encountered in an application where the shaft was disposed vertically or at an upright angle, and the load was effected by the constant pull of gravity on a weight, for example.
In other respects the structure of the embodiment of FIG. 8 is similar to that of the previous embodiment.
From the above it can be seen that I have provided novel and improved mechanical cam drives which are both simple in their structures, and which are especially adaptable for applications which require low or "zero" backlash. The embodiment of FIGS. 6, 7 and 9 also features the capability of high-speed operation and extended life, by virtue of the unidirectional rotation of the anti-friction rollers 120 and 122.
The disclosed devices are thus seen to represent a distinct advance and improvement in the field of mechanical transmissions.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS3296880 *Oct 18, 1965Jan 10, 1967Maroth Engineering CoRadial roller anti-friction transmissionUS3308674 *Jan 27, 1965Mar 14, 1967Maroth Arthur MRadial roller anti-friction transmissionUS3766788 *Aug 23, 1972Oct 23, 1973Norco IncRadial roller anti-friction transmission with eccentric bushingsUS3766800 *Jun 30, 1972Oct 23, 1973Narco IncVariable efficiency mechanical transmissionUS3779094 *Jun 12, 1972Dec 18, 1973Norco IncReversing nut for a diamond thread screwUS3792616 *Feb 7, 1973Feb 19, 1974Norco IncReciprocating driveUS4008625 *Dec 15, 1975Feb 22, 1977Norco, Inc.Floating nut constructionUS4022076 *Feb 17, 1976May 10, 1977Norco, Inc.Anti-backlash automatically reversing nut for a diamond thread screwUS4031765 *Mar 31, 1975Jun 28, 1977Norco, Inc.Reversing nut for diamond thread screwUS4198872 *Jul 28, 1978Apr 22, 1980Norco, Inc.Mechanical screw transmissionUS4199999 *Jul 28, 1978Apr 29, 1980Norco, Inc.Ball-type mechanical transmissionUS4343200 *Sep 8, 1980Aug 10, 1982James AlworthReversing attachment for diamond thread screwUS5191805 *Jan 10, 1992Mar 9, 1993Norco, Inc.Anti-friction nutUSRE28429 *Jun 10, 1974May 27, 1975 Lead screw and nutFR526586A * Title not availableGB1293430A * Title not availableGB190701044A * Title not availableJPH01153861A * Title not available* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS6459770 *Apr 18, 2001Oct 1, 2002Analogic CorporationBacklash-resistant drive assembly for collimator in a CT scannerUS20060117877 *Oct 28, 2005Jun 8, 2006Yasuhira InadaFeeding device and manufacturing method for rotation shaftUS20090133523 *Aug 28, 2008May 28, 2009Cheun Bok SongError-compensating bearing screw conveying deviceUS20100006302 *Jul 11, 2008Jan 14, 2010Baker Hughes IncorporatedLocking arrangement to store setting forcesUS20110232407 *Jul 27, 2009Sep 29, 2011Armin VerhagenHelical gearingUS20120174691 *Aug 19, 2010Jul 12, 2012Hiroyuki YamadaLinear actuatorUS20160025197 *Dec 21, 2012Jan 28, 2016J�zsef GulyasAn inescapable path to transform a form of motionWO2008046294A1 *Sep 29, 2007Apr 24, 2008Nanjing Kangni New Technology Of Mechantronic Co., Ltd.A selfadapting screw transmission mechanism with variable lead* Cited by examinerClassifications U.S. Classification74/441, 74/424.93International ClassificationF16H25/24, F16H25/22Cooperative ClassificationY10T74/198, F16H25/2003, Y10T74/19902, F16H25/2261European ClassificationF16H25/22C4Legal EventsDateCodeEventDescriptionAug 10, 1995ASAssignmentOwner name: NORCO, INC., CONNECTICUTFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:PARSONS, JOHN D.;REEL/FRAME:007566/0516Effective date: 19950622Sep 28, 1998ASAssignmentOwner name: BANKBOSTON, N.A. 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Patent US20060091676 - Supercharger coupled to a motor/generator unit - Google Patents
A device for handling and recovering of kinetic energy in a fluid is presented which basically features a bladed impeller (11). The impeller is operated by an electric engine (12) and acts as a centrifugal blower yielding energy to the air when the main engine is in a low boost phase; otherwise in case...http://www.google.com/patents/US20060091676?utm_source=gb-gplus-sharePatent US20060091676 - Supercharger coupled to a motor/generator unit
Publication number US20060091676 A1
Application number US 10/529,591
PCT number PCT/IB2003/004311
Also published as DE60315688D1, DE60315688T2, EP1554467A1, EP1554467B1, US7382061, WO2004029418A1
Publication number 10529591, 529591, PCT/2003/4311, PCT/IB/2003/004311, PCT/IB/2003/04311, PCT/IB/3/004311, PCT/IB/3/04311, PCT/IB2003/004311, PCT/IB2003/04311, PCT/IB2003004311, PCT/IB200304311, PCT/IB3/004311, PCT/IB3/04311, PCT/IB3004311, PCT/IB304311, US 2006/0091676 A1, US 2006/091676 A1, US 20060091676 A1, US 20060091676A1, US 2006091676 A1, US 2006091676A1, US-A1-20060091676, US-A1-2006091676, US2006/0091676A1, US2006/091676A1, US20060091676 A1, US20060091676A1, US2006091676 A1, US2006091676A1
Inventors Giuseppe Ferraro
Original Assignee Giuseppe Ferraro
Patent Citations (67), Classifications (26), Legal Events (4)
US 20060091676 A1
US2037402 * Dec 7, 1931 Apr 14, 1936 Leonard Taylor John Blower
US2355494 * Sep 19, 1941 Aug 8, 1944 Yingling Frank B Reversible rotary blower
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U.S. Classification 290/45
International Classification F02B39/10, B60L11/02, F04D25/06, F02B37/04, F01D15/10, F02B37/18, B61C9/38, F02C6/12, F04D25/04
Cooperative Classification F02B39/10, F02C6/12, F04D25/06, Y02T10/144, F01D15/10, F02B37/04, Y02T50/672, F04D25/045, F02B37/18
European Classification F02C6/12, F01D15/10, F04D25/04B, F02B39/10, F02B37/18, F04D25/06, F02B37/04


text:
Patent US4602209 - Switch-off circuits for transistors and gate turn-off thyristors - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsIn order to provide rapid turn-off of a transistor (or thyristor) having its emitter (or cathode) at a floating potential, on drive is removed from the base of the transistor T1 and almost simultaneously a switch SW1 is closed. This causes a proportion of the current which flows through a capacitor C...http://www.google.com/patents/US4602209?utm_source=gb-gplus-sharePatent US4602209 - Switch-off circuits for transistors and gate turn-off thyristorsAdvanced Patent SearchPublication numberUS4602209 APublication typeGrantApplication numberUS 06/605,804Publication dateJul 22, 1986Filing dateMay 1, 1984Priority dateJun 24, 1983Fee statusLapsedPublication number06605804, 605804, US 4602209 A, US 4602209A, US-A-4602209, US4602209 A, US4602209AInventorsBarry W. Williams, Patrick R. PalmerOriginal AssigneeWilliams Barry W, Palmer Patrick RExport CitationBiBTeX, EndNote, RefManPatent Citations (4), Non-Patent Citations (2), Referenced by (3), Classifications (12), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetSwitch-off circuits for transistors and gate turn-off thyristorsUS 4602209 AAbstract In order to provide rapid turn-off of a transistor (or thyristor) having its emitter (or cathode) at a floating potential, on drive is removed from the base of the transistor T1 and almost simultaneously a switch SW1 is closed. This causes a proportion of the current which flows through a capacitor C on turn-off of the transistor T1 to flow through a resistor R1 by way of the base of the transistor T1, thus providing a reverse base current which rapidly turns-off the transistor T1. In a practical implementation of this circuit the switching device is a transistor Toff and the circuit employs a self-timing approach in which removal of an "on" control signal from the gate of a field-effect transistor T7 automatically actuates the reverse current drive.
We claim: 1. A switch-off circuit for a main semi-conductor power switch having two power-conducting terminals and a control terminal, said circuit comprising source terminals for connection to a power source, load terminals for connection to a load, said switch being connected intermediate the source and load terminals such that the two power-conducting terminals of the switch form a series combination with the load terminals connected across the source terminals, said switch having one of its first or second power-conducting terminals at a floating potential and serving to conduct a main current by way of its two power-conducting terminals on application of an "on" drive signal to its control terminal, a capacitor connected in parallel with said two power-conducting terminals of said switch, and a secondary switching device connected to the control terminal of the said switch, whereby, on removal of said "on" drive signal from the control terminal of the said switch, the secondary switching device is turned on and a current is caused to flow from the capacitor to the secondary device by way of the control terminal of the said power switch, thus providing a reverse bias current which rapidly turns off the said switch.
2. Circuit according to claim 1, and a control device coupled to said main power switch and said secondary switching device such that, when a control signal is applied to the control device, said main power switch is caused to conduct the main current and the secondary switching device is turned off and, when the control signal is removed from the control device, said "on" drive signal is removed from the control terminal of the said main switch and the secondary switching device is automatically turned on to provide the reverse bias current for rapid turn-off of the said main power switch.
BACKGROUND OF THE INVENTION This invention relates to circuits for providing rapid turn-off of transistors and gate turn-off thyristors (gto's).
FIGS. 1a and 1b of the accompanying drawings show typical transistor switching circuit configurations using an npn transistor T1 (FIG. 1a) and a pnp transistor T2 (FIG. 1b) respectively. The transistor T1 or T2 is turned on by the application of current across the transistor base-emitter (b-e) junction, in the direction shown by the "on" arrow in FIGS. 1a and 1b. This causes the voltage across the transistor T1 or T2 to fall to near zero and the supply voltage V to be applied across the load causing current to flow from the supply V through both the load and the transistor T1 or T2. In each circuit example the transistor emitter terminal (e) remains at a fixed reference potential, either OV in the case of FIG. 1a or +V in the case of FIG. 1b. Removal of the forward base current will cause the transistor T1 or T2 to turn off. The diode D provides a path for the load current when the transistor T1 or T2 is turned off. For fast turn-off, reverse base current is applied, as shown by the "off" arrow in FIGS. 1a and 1b, which causes the base-emitter junction to cut off very quickly.
FIGS. 2a and 2b of the accompanying drawings show two further known transistor switching circuits using an npn transistor T1 (FIG. 2a) and a pnp transistor T2 (FIG. 2b) respectively, but in these cases the transistor emitter terminal is not at a fixed potential OV or +V. In these cases both the base and emitter change potential (relative to, say, the OV rail) when the transistor T1 or T2 switches on and off. The base and emitter are said to be at floating potentials. This effect necessitates more complex circuitry to control the transistor T1 or T2. It is therefore unfortunate that FIG. 2a forms the basis of a very commonly required configuration in bridge circuits. Complex and costly techniques exist for providing the necessary floating on and off base drive for the configurations shown in FIGS. 2a and 2b. These techniques usually involve the use of floating power supplies, optically transmitted control signals, pulse transformers, etc, all of which are necessary to provide voltage isolation for the base and emitter with respect to the OV or +V voltage rails.
A simple turn-on technique exists for the configurations of FIGS. 2a and 2b, as shown in FIGS. 3a and 3b. This involves the use of a pnp-npn Darlington transistor configuration comprising a pnp transistor T3, an npn transistor T5 and resistors R1 and R2 (FIG. 3a), or an npn transistor T4, a pnp transistor T6 and resistors R3 and R4 (FIG. 3b). The switching transistors T3, T4, T5 and T6 can be replaced by field-effect transistors, and the transistor T1 in FIG. 3a can be replaced by a gto, in possible variation of this circuitry. Turn-on is achieved by switching transistor T5 or T6 on by application of a turn-on current across the base-emitter junction which turns on transistor T3 or T4 which, in turn, turns on the main transistor T1 or T2. Simple turn-on is thereby achieved but no reverse base current can be provided for fast, efficient turn-off. This is a particular disadvantage where the device to be controlled is a gto since gto's must have reverse gate current for turn-off.
It is an object of the invention to provide a simple technique for achieving rapid turn-off of a bipolar or field-effect transistor or gate turn-off thyristor (gto) having an emitter or cathode at a floating potential utilising a reverse base or gate current.
SUMMARY OF THE INVENTION According to the invention the circuit comprises a main bipolar or field-effect transistor or gate turn-off thyristor for conducting a main current by way of its collector-emitter or anode-cathode path on application of on drive to its base or gate, a capacitor connected in parallel with the collector-emitter or anode-cathode path of the main transistor or thyristor, and a switching device coupled to the base or gate of the main transistor or thyristor such that, on removal of on drive from the base or gate of the main transistor or thyristor, the switching device is turned on and a current is caused to flow from the capacitor to the switching device by way of the base or gate of the main transistor or thyristor, thus providing a reverse base or gate current which rapidly turns off the main transistor or thyristor.
By use of this technique a very significant improvement in turn-off time is achieved as compared with conventional circuits, such as that illustrated in FIG. 3a, in which no special provision are made for rapid turn-off. Furthermore the technique is particularly applicable to the turn-off of a gto for which the provision of a reverse gate current is essential. The circuit may take on many different forms depending on the particular application, and may be integrated in a single semiconductor substrate in which case the various components will be formed by different regions of the substrate and many not be physically separated from one another.
In one form of circuit in accordance with the invention a control device is coupled to the main transistor or thyristor and the switching device such that, when a control signal is applied to the control device, the main transistor or thyristor is caused to conduct the main current and the switching device is turned off and, when the control signal is removed from the control device, on drive is removed from the base or gate of the main transistor or thyristor and the switching device is automatically turned on to provide the reverse base or gate current for rapid turn-off of the main transistor or thyristor. This circuit utilises a self-timing approach in which rapid turn-off is automatically initiated on removal of the "on" control signal. The control device may be a field-effect transistor for example.
The circuit may include one or more diodes connected across the base-emitter or gate-cathode junction of the main transistor or thyristor in order to limit the reverse base-emitter or gate-cathode voltage of the main transistor or thyristor. Furthermore, where the switching device is constituted by a first switching transistor, a second switching transistor may be connected in anti-parallel with the first switching transistor such that, when the second switching transistor is turned off, the first switching transistor is turned on to conduct the reverse base or gate current for rapid turn-off of the main transistor or thyristor.
In a development of this form of circuit, in which the switching device is constituted by a switching transistor, a further switching transistor is connected to the switching device to form a Darlington configuration providing a high level of reverse base or gate current for rapid turn-off of the main transistor or thyristor.
In a further development the connections to the main transistor or thyristor and the switching device are such that the base-emitter or gate-cathode junction of the main transistor or thyristor is reverse biased when the switching device is turned on. This is desirable for reliable operation of the transistor or gto.
In another form of circuit in accordance with the invention a supplementary control device is coupled to the switching device such that, when a supplementary control signal is applied to the supplementary control device on removal of the control signal from the main control device, the supplementary control device is turned on to allow a current to flow which causes the switching device to turn on. Such an arrangement enables the power losses to be minimised in the circuit when the main transistor or thyristor is conducting.
In a further form of circuit in accordance with the invention a main transistor and main gate turn-off thyristor are provided in combination, the anode-cathode path of the main thyristor being connected in parallel with the collector-base or anode-gate junction of the main transistor such that on drive is supplied to the main transistor by the main thyristor when the main thyristor is turned on, and such that, when the switching device is turned on after removing gate drive from the main thyristor, a current is caused to flow from the capacitor to the switching device by way of the base or gate of the main transistor and the gate of the main thyristor, thus providing reverse base/gate and gate currents for rapid turn-off of both the main transistor and the main thyristor.
DETAILED DESCRIPTION OF THE DRAWINGS FIG. 4 shows a transistor switching circuit configuration using an npn transistor T1 for supplying a main current by way of its collector-emitter path to a load. The base and emitter are at floating potentials, that is to say their potentials change relative to the OV rail when the transistor T1 switches on and off. The diode D provides a path for the load current when the transistor T1 is turned off. In order to achieve rapid turn-off of the transistor T1 by providing reverse base current on turn-off, a capacitor C is connected in parallel with the collector-emitter path, and a switch SW1 is connected to the base of the transistor T1 by way of a resistor R1. A normal turn-on circuit, for example as shown in FIG. 3a, is used to provide forward base current for turn-on of the transistor T1.
For turn-off, on drive is removed from the base of the transistor T1 and almost simultaneously switch SW1 is closed. This causes a proportion of the current which flows through capacitor C on turn-off of the transistor T1 to flow through the resistor R1 by way of the base of the transistor T1, thus providing the reverse base current necessary for fast transistor turn-off. The current through the resistor R1, and hence the reverse base current, decreases as the capacitor C is charged up. In this application the capacitor C performs the dual function of providing reverse base current and of reducing switch-off losses in view of the fact that the capacitor serves to shunt a proportion of the current supply to the load as the transistor T1 switches off, thus ensuring that the transistor T1 is not unduly stressed on switch-off.
A switching circuit utilising a capacitor for reducing switch-off losses is known and such a circuit is shown in FIG. 5. This configuration incorporates a capacitor C, a diode D3 and a resistor R5 which serve to shunt current to the load when the transistor T1 turns off in order to reduce the power through the transistor on turn-off. However, it should be stressed that no reverse base current is provided by such a circuit configuration.
FIG. 4 is intended to illustrate the basic principles of the invention and various practical implementations of this concept will now be described with reference to the remaining drawings, the various circuits offering different advantages and features adapted to particular applications.
In the circuit illustrated in FIG. 6a, the switch SW1 is replaced by a switching device in the form of a pnp switching transistor Toff which is intended to turn on on turn-off of the main transistor T1 in order to provide the required reverse base current in the transistor T1. The circuit employs a self-timing approach in which removal of an "on" control signal from the gate of a control device in the form of a field-effect transistor T7 automatically actuates the reverse current drive circuit. An npn transistor T8 is connected with its base-emitter path in anti-parallel with the base-emitter path of the transistor Toff, and a further field-effect transistor T9 is connected intermediate the transistors T7 and T8 with its gate biased by resistors R1 and R2. When the transistor T7 turns off on removal of the "on" control signal, the transistor T9 turns off, the transistor T8 turns off and the main transistor T1 begins to turn off. When the transistor T8 turns off, the current drawn by the resistor R3 through the transistor Toff from the capacitor C turns on Toff, and Toff conducts a large current via the resistor R4, thus providing the required reverse base current in the transistor T1, as indicated by the arrows in FIG. 6a. A diode D1 and Zener diode D2 are connected across the base-emitter junction of the main transistor T1 to limit the reverse b-e junction voltage of the transistor.
FIG. 6b illustrates a modification of the circuit of FIG. 6a in which an npn transistor T10 is used in conjunction with the pnp transistor Toff to form a Darlington configuration having a high reverse current capability for turn-off of the main transistor T1. In either of these circuits, or in any of the circuits still to be described, the pnp transistor Toff can be replaced by a p-channel field-effect transistor. Furthermore an npn transistor or an n-channel field-effect transistor can be used in similar circuitry for turn-off of the pnp transistor T2 of FIG. 3b.
If the turn-off circuit resistors R3 and R4 are connected to a potential slightly lower than the OV rail, as shown in the alternative circuits of FIGS. 7a and 7b, the transistor T1 has its b-e junction reverse-biased in the off-state. This is a desirable condition for robust and reliable transistor operation (and for operation of a gto where such a device is used instead of the transistor T1).
In the circuits of FIGS. 6a, 6b, 7a and 7b, the resistor R3 draws current through the transistor T9 when the main transistor T1 is on. If the duty cycle of the transistor T1 is high, the power dissipated in the resistor R3 may be high. In order to reduce these losses and hence provide energy saving, arrangements such as those illustrated in FIGS. 8a and 8b may be utilised. In these circuits a supplementary control device in the form of a field-effect transistor T11 is connected between the resistor R3 and the OV or -V rail, and an "off" control signal Q is applied to the gate of the transistor T11 in order to turn the transistor T11 on when the "on" control signal Q is removed from the gate of the transistor T7 in order to turn that transistor T7 off. This then enables the transistor Toff to be turned on for rapid turn-off of the transistor T1. Since the transistor T11 is turned off when the main transistor T1 is turned on, current is no longer drawn through the transistor T9 by the resistor R3 when the main transistor T1 is on and significant energy saving results. The circuit of FIG. 8b also incorporates the feature of reverse b-e junction biasing.
The main transistor T1 may be replaced by a gto in any of the above described circuit arrangements which are well adapted to the turn-off of a gto since they provide the necessary reverse gate current. FIG. 9 shows a circuit in accordance with the invention utilising a gto G1 in which conventional turn-on circuitry is utilised for turning on the gto G1, and a gate resistor R10 is provided to limit the reverse gate current. When a control signal is applied to the gate of the field-effect transistor Toff, the transistor Toff is turned on thus providing a flow of current from the capacitor C to the transistor Toff by way of the gate of the gto G1 and the resistor R10, this reverse gate current ensuring rapid turn-off of the gto G1 after removal of the gate drive.
FIG. 10 shows a circuit utilising a gto-npn transistor switch combination G1, T1. The gto G1 is used to provide the on-base current for the npn transistor T1, the gto G1 itself being turned on by conventional turn-on circuitry. Turn-off is achieved by turning on the transistor Toff after the gto gate drive is removed. Both the gto G1 and the transistor T1 are turned off by the resultant reverse current which flows from the capacitor C, as shown by the arrow in FIG. 10. In this circuit the diodes D4, D5, D6 and D7 perform the same functions as the diodes D1 and D2 in the circuits of FIGS. 6a and 9. The diode D8 and resistor R11 also provide added protection for the transistor T1.
It has been found that, when the circuit of FIG. 8a, for example, is used with a 150V dc supply and a 20A load current, the collector current of the transistor T1 decreases from 20A to 0A, after a storage time of 1.5 microseconds, with a fall time of 0.2 microseconds, and the collector voltage increases from near zero volts to 150V dc during the fall time. These results were obtained with a switching frequency of 2 kHz and a snubber capacitance of 0.2 microfarads, and compare with a current fall time of 1 microsecond and a storage time of 4 microseconds when a transistor was turned off under similar conditions but without utilising the reverse base current technique of the invention. The improved performance results from a 3A reverse base current provided for fast turn-off. Particular advantages are obtained by such an arrangement since, the faster the current fall time, the lower the turn-off switching losses. This also enables a smaller value snubber capacitance to be utilised, as well as allowing the transistor to be operated at a higher frequency than would be possible if the reverse base current technique was not used. The turn-off circuitry is therefore of particular application in choppers and inverters.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS4295059 *Mar 30, 1979Oct 13, 1981General Electric CompanyHigh gain latching Darlington transistorUS4549095 *Nov 15, 1982Oct 22, 1985Sgs-Ates Componenti Elettronici S.P.A.Control circuit for switching inductive loadsDE2403687A1 *Jan 24, 1974Aug 7, 1975Licentia GmbhAbschaltung eines leistungstransistorsGB2037114A * Title not available* Cited by examinerNon-Patent CitationsReference1Hammond et al., "High Power Vector Summation Switching Power Amplifier Development", Power Electronics Specialists Conference, 1981, Boulder Co. USA, (Jun. 29-Jul. 3, 1981), pp. 267-272 (Fig. 4).2 *Hammond et al., High Power Vector Summation Switching Power Amplifier Development , Power Electronics Specialists Conference, 1981, Boulder Co. USA, (Jun. 29 Jul. 3, 1981), pp. 267 272 (Fig. 4).* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS4945467 *Feb 26, 1988Jul 31, 1990Black & Decker Inc.Multiple-mode voltage converterUS5010439 *Jun 12, 1989Apr 23, 1991Sgs-Thomson Microelectronics S.R.L.Control circuit for the clamping voltage of an inductive load driven by a power device in a high side driver configurationUS20110273220 *May 3, 2011Nov 10, 2011Feng LinOptimal mosfet driver circuit for reducing electromagnetic interference and noise* Cited by examinerClassifications U.S. Classification323/351, 327/442, 323/289, 327/428, 327/432, 327/377International ClassificationH03K17/0412, H03K17/732Cooperative ClassificationH03K17/04126, H03K17/732European ClassificationH03K17/0412D, H03K17/732Legal EventsDateCodeEventDescriptionOct 2, 1990FPExpired due to failure to pay maintenance feeEffective date: 19900722Jul 22, 1990LAPSLapse for failure to pay maintenance feesFeb 20, 1990REMIMaintenance fee reminder mailedRotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google


text:
Michael Daffertshofer - Semantic Scholar
Michael Hennerici82
Julien Ed Bogousslavsky11
97Michael Hennerici
16G Tsivgoulis
14H. Baezner
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