US3454137A - Lubrication device for electrostatic actuators - Google Patents

Description

y 8, 1 NIYAZI AYGUN ETAL I 3,454,137

- LUBRICATION DEVICE FOR ELECTROSTATIC ACTUATORS Filed Dec. 23, 1966 I On [lllll l-lll D S m a m m. m o N K T Y. .T EA A .V R v W M n w R T MZ United States Patent 3,454,137 LUBRICATION DEVICE FOR ELECTROSTATIC ACTUATORS Niyazi Aygun and Frederick G. Krebs, Dayton, Ohio, as-

signors to The National Cash Register Company,

Dayton, Ohio, a corporation of Maryland Filed Dec. 23, 1966, Ser. No. 604,331 Int. Cl. F16n 9/04 US. Cl. 184-14 1 Claim ABSTRACT OF THE DISCLOSURE A lubricating device having a lubricating stick engaging the periphery of the drum of an electrostatic actuator employing the Johnsen-Rahbeck effect. As the drum is rotated, the stick is reciprocated along a line which is parallel to the longitudinal axis of the drum to trace a helical band of lubricating film on the periphery.

This invention relates to a device for lubricating the peripheries of shafts and drums, and more specifically it relates to a lubrication device for electrostatic actuators of the type employing a rotating drum and an external brake band.

This type of electrostatic actuator can be used as a clutch, and, when so used, it includes, essentially, a rotating drum and a thin metal band. The drum is coated with a highly polished layer of dielectric material of high resistivity, and the metal band is wrapped around at least a portion of the periphery of the drum, one end of the band being fixed and the other end of the band being secured to a spring to resiliently hold the band against the drum. The drum is rotated and is charged with a potential of one polarity. With no charge on the band, the drum continues to rotate in slipping engagement with the band; however, when the clutch is actuated, a charge of opposite polarity is placed upon the metal band, and the band is attracted to the drum and is held in driving engagement therewith by an electrostatic force due to the Johnsen-Rahbeck effect. The end of the band secured to the spring is pulled in the direction of rotation of the drum to do the desired work. When the charge is removed from the metal band to deactuate the clutch, the spring restores the band to a home position in readiness for the next cycle of operation.

Lubricating the surface of the drum in an electrostatic actuator of the type mentioned in the previous paragraph has been a problem. The lubrication is necessary to minimize the wear between the metal band and the periphery of the drum, and yet the lubrication should not interfere with the driving engagement between the band and the drum. Reliable operation of such an actuator requires a lubrication film thickness of about 20 to 30 microinches. Any contaminating particles in the lubrication film tend to destroy the mating surfaces of the drum and the band. If a stationary stick of lubricant is used to press against the rotating drum, contaminating particles become lodged in the stick, causing excessive, uneven wear on the stick itself. Various types of scraper cleaners and brushes were tried, but none of them provided the clean regenerative film produced by the lubrication device of this invention.

Applicants lubricating device includes a lubricating stick holder means which is movably mounted in a frame to enable one end of the stick to be directed at the periphery of the rotating drum. Means are also provided for reciprocating the holder means along a line which is parallel to the axis of the rotating drum, enabling a relatively small lubricating stick to effectively lubricate the "ice entire periphery of the rotating drum. Because the stick is being continuously moved, a surprisingly clean lubricating film is deposited on the drum, enabling reliable operation of the electrostatic actuator. Any portions of the lubricating film which are damaged by contamination particles are soon repaired by the constant regenerative action of the moving lubrication block or stick. As the drum rotates, the lubricant stick traverses the periphery of the drum to trace a helical band of lubricating film thereon. Successive passes of the stick are effective to fill in the areas between adjacent helical bands, resulting in a continuous lubricating film being deposited on the periphery of the drum.

Accordingly, the objects of this invention are:

(a) To provide a device for applying a thin film of lubricant to the periphery of a rotating member and for regenerating this film;

(b) To provide a device for lubricating the mating surfaces between the periphery of a rotating member and a mating band engaging at least a portion of said periphery and to provide a means for minimizing the wear-' ing effect of contaminating particles on said mating surfaces;

(c) To provide a device for maintaining a lubricating film of minute thickness between the mating surfaces of an electrostatic actuator as required for reliable operation of the actuator; and

(d) To provide a device for maintaining a lubricating film between the mating surfaces of an electrostatic actuator so that variations in the film thickness due to the non-homogeneous character of the lubricating stiok used to apply the film will be minimized.

These and other objects and advantages will become more readily understood in connection with the following description and the drawings, in which:

FIG. 1 is a plan view of the bottom of an electrostatic actuator, showing the means for applying a thin film of lubricant to the periphery of the rotating member of the actuator; and

FIG. 2 is an elevational view in cross-section which is taken along the line 22 of FIG. 1, showing more details of the lubricating means of this invention.

The lubricating means 10 of this invention is shown in use with an electrostatic actuator 12, of the band clutch type, which is shown in FIGS. 1 and 2. The actuator 12 is of the type which employs a rotating steel drum 14 supported on a shaft 16, which is supported in electrical insulator bushing members 18 and 20 (FIG. 1). The shaft 16 is provided with a reduced diameter portion 22, which fits into the bushing 20, which is conveniently retained in a planar support member 24. A locking collar 26, secured to the shaft 16 on one side of the member 24 in conjunction with the shoulder formed by the reduced diameter portion 22 located on the other side of the member 24, is efiective to restrain the drum 14 against axial movement in the planar support members 24 and 28, which are in spaced, parallel relation.

The steel drum 14, which forms a major part of the electrostatic actuator 12, has a periphery which is coated with a layer 30 of highly polished dielectric material of high resistivity. Aside from having the desired electrical properties to obtain the Johnsen-Rahbeck effect, the layer 30 should also be selected to have a coeflicient of expansion similar to that of the metal of the drum. Historically, the Johnsen-Rahbeck effect relates to an attractive force which exists whenever a highly polished surface of metal is brought into engagement with a similarly polished surface of lithographic stone and a potential dilference is applied between the metal and the stone. A detailed discussion of the Johnsen-Rahbeck effect, with particular reference to its application to electrostatic clutches, may

3 be found in the article Electrostatic Clutches, Dudding and Losty, G. E. C. Journal, vol. 33, No. l, 1966.

The other major part of the electrostatic actuator 12 shown includes a metal band 32, which is in sliding engagement with a portion of the periphery of the drum 14. One end of the band is fixed at 34, and the other end is secured to a spring 36, which keeps the band in sliding contact with the periphery of the drum as it is rotated in the direction indicated by the arrow A (FIG. 2).

An electrical potential of one polarity is applied to the drum 14 via a brush 38 on the shaft 16, and, when the electrostatic device 12 is to be actuated, a potential of opposite polarity is applied to the band 32 via a contact 40 to create the desired attractiv electrostatic force which causes the band 32 to be rotated with the drum 14, thereby pulling the end 42 of the band 32. When the end 42 is pulled, work can be done; this is shown diagrammatically by the lever 44, which is pivotally mounted between its ends on a support 46. One end of the lever 44 is pivotally secured to a block 48, which is secured to the end 42 of the band 32. When the potential is removed from the band 32, the band is released from the rotating drum, and the spring 36 returns the band to a home position in readiness for the next cycle of operation.

As previously mentioned, supplying a thin film of lubricant to the periphery of the drum 14 of the electrostatic actuator 12 is extremely important for reliable functioning of the actuator 12. The lubricating means 10, shown in FIGS. 1 and 2, provides such a thin film.

The lubricating means includes a lubricant stick or block 50, which is slidably mounted in a holder 52 and is directed in a radial line toward the axis of the drum 14. An adjustable screw 54 is used to vary the tension on a spring 56, which urges the stick 50 out of the holder 52 and against the coating on the drum 14.

The holder 52 is movably mounted in the frame for reciprocating movement parallel to the axis of the drum 14, as follows. The holder 52 is provided with a bore enabling it to be slidably mounted on a rod 58, which is parallel to the axis of the drum 14 and which rod is conventionally restrained against axial movement in the support members 24 and 28. The ends of the rod 58 are mounted in conventional insulator bushings 59 to isolate the rod and the holder 52 from the support members 24 and 28. The holder 52 is also supplied with a second aperture (parallel to the first), in which a standard, reverselythreaded, transversing shaft 60 is mounted. The ends of the shaft 60 are rotatably mounted in conventional insulator bushings 62 and 64 to isolate the shaft 60 from the support members 24 and 28. A conventional pawl 66, secured to the holder 52, engages the grooves of the transversing shaft 60 in the usual manner.

When the transversing shaft 60 is rotated, the holder 52 reciprocates between the support members 24 and 28, enabling the small lubricating stick 50 to also reciprocate across the periphery of the drum 14. As the drum rotates, the reciprocating lubricant stick 50 deposits a narrow helical band of lubricant on the periphery thereof. Upon successive passes of the stick 50, the areas between adja cent helical bands of lubricant formed on the periphery will be filled, forming a continuous film thereon. Any portions of th lubricating film which are damaged either by contaminating particles or by abrasive action between the band 32 and the drum 14 are soon repaired by the constant regenerative action of the moving lubrication stick 50. Because the shear forces acting on the face of the lubricating stick when it is engaging the drum 14 are composed of components acting at right angles to each other, and because one of these components constantly changes direction (via the transversing shaft), any wear particles which accumulate are kept in constant motion, so that they do not become imbedded in the face of the stick. Temperature build-up of the stick 50 is also minimized by preventing particles from becoming imbedded in the face of the stick 50.

The transversing shaft may be rotated independently of the shaft 16 by a separate driving means (not shown), or the shaft 60 may be connected to rotate with the shaft 16 by meshing gears 68 and 70, which are fixed to rotate with the shafts 60 and 16, respectively.

The particular lubricant employed in the stick 50 is of course dependent upon the type of electrostatic actuator used, the type of dielectric material used, the speed of the rotating drum, and the like. For illustrative purposes, the coating 30 applied to the drum 14 in the embodiment shown was barium titanate applied by the flame spraying technique, and the lubricant used in the stick 50 was a mixture of tetrafiuoroethylene and molybdenum disulfide.

What is claimed is:

1. A lubricating apparatus for lubricating the periphery of a rotating member of an actuator device of the electrostatic type, comprising:

frame means;

holder means having a lubricant stick slidably mounted therein and extending outwardly therefrom;

means for movably mounting said holder means in said frame means enabling said lubricant stick to engage said periphery;

and means for reciprocating said holder means along a line substantially parallel to the axis of said rotating member as said member is rotated to thereby lubricat said periphery;

said holder means having adjustable means to resiliently urge said lubricant stick out of said holder means to engage said periphery;

said means for movably mounting said holder means comprising a rod member positioned in said frame means in spaced parallel relationship with the axis of said rotating member;

said holder means having a hole passing therethrough to slidably receive said rod member, and also having a second hole in spaced parallel relationship with said first-named hole;

saidmeans for reciprocating said holder means comprising a reversely-threaded transversing shaft rotatably mounted in said frame means in spaced parallel relationship with said rod member, said transversing shaft being slidably mounted in said second hole, and pawl means operatively connecting said holder means with said transversing shaft to reciprocate said holder means as said transversing shaft is rotated,

and connecting means operatively connecting said transversing shaft with said rotating member to rotate said shaft whenever said rotating member is rotated,

said lubricating apparatus being effective to provide a clean, regenerative film of lubricant on said periphery.

References Cited UNITED STATES PATENTS 656,366 8/1900 Nelles 118242 X 1,875,467 9/1932 Knoerzer et al 7457 X 2,586,014 2/1952 Dunphy 15306.1 X 2,692,738 10/1954 Seaman 74-57 X 2,850,908 9/1958 Foster 19221.5 X 2,923,390 2/1960 Fitch 19221.5 X

LAVERNE D. GEIGER, Primary Examiner.

EDWARD J. EARLS, Assistant Examiner.

US. Cl. X.R.

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