Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
2001-11-14
2003-10-21
Hannon, Thomas R. (Department: 3682)
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
C074S467000
Reexamination Certificate
active
06634246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recirculating-ball nut and screw set with lubricating means, which is suitable for use in industrial robots, semiconductor fabricating equipments, precision instruments, machine tools, and so on.
2. Description of the Prior Art
The linear motion guide units have been conventionally incorporated in the parts or components movable back and forth, which are used extensively in engineering fields as diverse as industrial robots, semiconductor fabricating equipments, inspection instruments, machine tools, and so on. The recently remarkable development in mechatronics technology extensively requires linear motion guide units because of high precision, high speed, compactness and so on. Moreover, the linear motion guide units recently have become required to meet with a need of maintenance-free, along with high precision and high speed in operation. To cope with the maintenance-free demands, the linear motion guide unit has required the self-lubrication of long-lasting service life on its relative sliding areas.
A recirculating-ball nut and screw set for the linear motion guide units shown in
FIGS. 14 and 15
is conventionally well known and, for example, as disclosed in Japanese Patent Laid-Open No. 273552/1997. The prior recirculating-ball nut and screw set in
FIGS. 14 and 15
is mainly comprised of a screw shaft
1
made around an outer periphery
13
thereof with a helical external groove
3
extending lengthwise of the screw shaft
1
, a ball nut
2
fit loosely over the screw shaft
1
and provided on an inner surface
12
thereof with a helical internal groove
14
confronting the helical groove
3
of the screw shaft
1
, balls
7
charged to roll in a raceway
15
defined between the confronting helical grooves
3
and
14
, and a return guide
4
allowing the balls
7
to recirculate from one end to the other end of the ball nut
2
. The ball nut
2
is composed of a flange
6
made with bolt holes
11
to fasten any object such as appliances, bases, parts, components, and so on thereto, and a hollow cylinder
17
having the helical internal groove
14
on the inner surface
12
thereof. The return guide
4
is communicated at its opposite ends to the raceway
15
through connecting port formed in the ball nut
2
and also secured to a flat area
20
on the hollow cylinder
17
of the ball nut
2
by means of a fastener
8
, which is held with machine screws
19
.
The ball nut
2
has a lubricant supply port
9
threaded at
18
, where a lubricant line, not shown, is connected to feed lubricant to the helical grooves
3
and
14
and balls
7
. Moreover, the recirculating-ball nut and screw set is provided with either wiper seals
5
or labyrinths. On forward and aft ends of the nut
2
there are annular recesses
16
in which the wiper seals
5
fit, each to each recess, to keep foreign matter such as dust and dirt from invasion inside the nut
2
, especially inside the raceway
15
.
There are also well known linear motion guide units with onboard lubricant plates, for example as disclosed in Japanese Patent Laid-Open No. 27861/2000, in which a slider with onboard lubricant plates fits over a round track shaft for sliding movement and any lubricant plate may be applicable without any modification on basic design specifications and also installed detachably in the slider. The lubricant plate is usually made of a sintered resinous component of cellular structure, which is impregnated with any lubricant and secured onto a core metal. The sintered resinous component is fabricated by heating finely powdered synthetic resin under pressure in a design mold. Each lubricant plate is held on a carriage of the slider, with interposed between the core metal and an end cap, which are arranged on any one of the forward and aft ends of the slider. Thus, the lubricant plates are allowed to travel relatively to the round track shaft, with keeping sliding engagement with at least raceway grooves on the track shaft.
Another type of the linear motion guide unit is disclosed in Japanese Patent Laid-Open No. 35038/2000, in which the slider with onboard lubricating plate assemblies fits over the round track shaft for sliding movement and installed in a large bore formed in appliance housing. The slider is also kept against escape out of the track shaft by means of retaining rings. The lubricating plate assemblies are each enclosed in a case and composed of a lubricant plate of sintered resinous component having cellular structure impregnated with lubricant, and an end seal. The lubricant will ooze little by little from the lubricant plate to lubricate the round track shaft as the slider moves along the round track shaft.
A recirculating-ball nut and screw set with onboard lubricating means is also known, for example disclosed in Japanese Patent Laid-Open No. 81103/2000, in which lubricant-containing polymer members are mounted on a ball nut, with coming into sliding contact with only the outermost diametral periphery of the round track shaft. When the slider moves along the round track shaft, the lubricant-containing polymer members slide on the round track shaft without scraping away the lubricant deposited in the grooves. Thus, the lubricant always remains accumulated in the grooves where the balls run through there.
In Japanese Patent Laid-Open No. 184683/1998 there is disclosed a linear motion guide unit having incorporated with a lubricant supply means, which includes a lubricant applicator coming into a sliding engagement with a round track shaft to apply the lubricant thereto, a lubricant occlusive body arranged near the lubricant applicator in a casing to store the lubricant while feed the lubricant to the lubricant applicator, and lubricant-metering means to control an amount of lubricant to be transferred to the lubricant applicator from the lubricant occlusive body.
Meanwhile, as the linear motion guide units such as linear rolling motion guide units, recirculating-ball nut and screw set and the like are recently finding a growing variety of applications in diverse fields, they become increasingly used under unfavorable operating conditions or adverse environments, for example, where no replenishment of lubricating oil is allowed, much dirt and debris contamination may occur and there is abnormally high in temperature or moisture. In recent years the linear motion guide units are needed to work in any clean room where the occurrence of dirt and debris has to be staved off to keep the desired cleanliness. Because of the current tendency as stated earlier, much attention has been given the development of the linear motion guide units having no fear of lubrication failures even under the severe operating conditions where it is very hard to achieve the normal lubrication. For the recirculating-ball nut and screw set, especially any maintenance-free lubrication system is needed and so many kinds of the lubrication systems have been heretofore devised to be installed in the recirculating-ball nut and screw set.
Nevertheless, many prior lubrication systems are installed on any one of forward and aft ends of the recirculating-ball nut and screw set, and complicated in construction, very tough to produce them, needed to modify the specification in compliance to the design of the ball nut and screw set to which the lubrication system is applied, and also troublesome to use. Recent advances in the various equipments such as semiconductor fabricating equipments and the like result in the diversity and higher speed of the linear motion guide units. Even if any periodic lubrication were ensured, there would be no possibility of lubrication failure led to any breakage or premature age. However, the piping work for lubrication system is tedious and the current operating situations make it even tougher to ensure that lubricant is supplied evenly into all the sliding surfaces. Thus, it remains a major challenge to develop a recirculating-ball and screw set that is maintenance-free in lubrication and also less in
Ishihara Toyohisa
Ohya Yasumasa
Browdy and Neimark , P.L.L.C.
Hannon Thomas R.
Nippon Thompson Co. Ltd.
Van Pelt Bradley J.
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