MOBILE GROUNDING DEVICE
Technical Field
The present invention relates to a grounding device,
more particularly to a mobile grounding device for dissipating static charges
of movable or non-movable objects to the ground.
Background Art
With the rapid miniturisation trend of the
microchips in the electronics industry, electrostatic discharge (ESD) has
become one of the major considerations in improving product quality and
reducing rejects due to such electrostatic discharge (ESD) damage. The
management of electrostatic discharge (ESD) control has already become a very
important and an indispensible function to fight against such ESD damage in a
highly competitive, high technology and fast-moving electronics manufacturing
industry globally.
Typically in an ESD control program, the grounding
of all materials, people and machines are necessary in order to eliminate or
minimize the occurrence of electrostatic discharge (ESD) events in an
ESD-sensitive electronics assembly work environment. The grounding of carts and
trolleys or other moving or non-moving apparatus are without exemption. There
are various prior arts that describe the applications and use of many special
moving or stationary grounding devices to-date.
US Patent 2125378 describe a grounding device that
attaches to the metallic portion of a vehicle to drain any accumulated static
charge from the vehicle (truck) to the ground. However, the invention possesses
the following shortcomings or limitations:
-Connecting chain flexible in one plane only in
order to hold the conductive wheel in the up-right position.
-Design of the connecting means is rather complex
and expensive as each connecting parts of the chain is complicated.
-Limitation in uni-directional movement design not
suitable for use in carts, trolleys, etc where movement in all directions are
required.
US Patent No 6327131 B1 describes a transportation
apparatus which includes an electrically conductive cart, an electrically
conductive pad coupled to the electrically conductive floor to ground the cart,
an electrically conductive cable coupled to the cart, and a fastening device
coupled the pad to the cable. The cart remains grounded by the electrically
conductive pad when the cart is transporting the sensitive components from one
location to another. However, the invention possesses another different set of
shortcomings as follows:
-The pad is flat & bulky thereby causing high
frictional and abrasive dragging action when the cart transports components
across an electrically conductive or static dissipative floor. The dragging of
the conductive or static dissipative pad not only create scratch lines
particularly over heavy traffic area, it also causes particles contamination in
today's many clean manufacturing environment especially in disk-drive, wafer
fabrication and other ultra-clean manufacturing environment.
-The complete connecting system of the pad involves
quite a number of material components and joining mechanism thereby lacking
attractiveness for a large scale commercial implementation.
US Patent 6357767 describes a grounding device that
attaches to the axle of a wheel to drain away any accumulated static charge
from the moving apparatus to the ground. However, there are following
shortcomings or limitations in real-life use:
-When the cart moves, the non-moving static
dissipative tubing 'pressing' on the floor creating a continuous abrasive
action that will cause scratch marks on the floor especially the cart moves
from a rough floor surface to a smooth clean surface of various floor
conditions. This is more prominent especially the cart moves from a wet floor
vicinity where sandy dirts are easily pick up by the non-rotatable static
dissipative tubing and subsequently drag on a wet or dry clean floor when the
cart enter from outside into the inside of a building after rain.
-When dragging the static dissipative tubing on a
static dissipative or conductive flooring of today's popular 'conductive vein'
type, there must be sufficient force or pressure applied on the floor to
achieve a fool-proof or fail-proof electrical connection. Sufficient bending
pressure or sufficient bending force of the polymer on a consistent basis is
difficult to achieve based on such design of the prior art. In fact, the prior
art failed to address such deficiency during real-life use of the product.
Therefore, further research is needed in developing
a useful grounding device that not only capable of moving in all directions,
frictionless or abrasion-free, it must also be low cost and cheap to produce to
achieve a commercially feasible undertakings.
Summary of Invention
The invention encompasses an unique spring-like
or flexible clamp attaches to a roller through its cramping force of its 'long
neck' or 'long claws' design.
The 'long neck' or 'long claws' structure design
acts as a pivotal lever to provide 'ease of turning' for a smooth drag whenever
the roller is in an unfavorable resting position as shown in Figure 1a.
There is no ball bearing, no screw, no bolt &
nut, no adhesive and no rivet is required in such unique 'long claws' design
that can be easily and quickly attached onto any bar-like or rod-like structure
of a movable or non-movable object.
The invention makes use of the weight of the
metallic roller to provide adequate gravitational pressure exerted on the floor
to achieve a good electrical contact between the grounding device and the
conductive floor consistently.
Optionally, a replaceable conductive or static
dissipative elastic band can be wrapped on the metallic roller or inserting a
static dissipative tubing onto such metallic roller as shown in Figure 2a. This
is to improve the noise pollution of the metallic roller during use and to
provide a more effective electrical contact when resting on the 'conductive
vein' type of conductive/dissipative floor in real-life use.
The mobile grounding device can be hooked onto a
hooked clip to achieve a chainless grounding system as shown in Figure 3.
Alternatively, the mobile grounding device can
also be hooked on to a hanging conductive cord to achieve a free-moving
grounding system as shown in Figure 4.
Optionally, the conductive or static dissipative
roller is mounted with a brush to clean its surface during use to maintain good
electrical property of the roller.
The invention achieve a very simple, durable,
reliable and low cost solution to uniquely drain static charge from moving cart
or trolley or apparatus to ground which the prior arts failed to addressed.
Description of Drawings
Figure 1a is a perspective view of a mobile
grounding device in accordance to the present invention showing the roller in
an unfavorable resting position;
Figure 1b is a perspective view of the mobile
grounding device as shown in Figure 1a showing the ease of turning of the
roller from the unfavorable resting position to the favorable position;
Figure 1c is a perspective view of the mobile
grounding device as shown in Figure 1a showing the roller turned to a favorable
rolling position;
Figure 2a shows a perspective view of the roller
wrapped with an elastic conductive or dissipative tubing;
Figure 2b shows a perspective view of the roller
wrapped with at least two elastic conductive or dissipative bands;
Figure 3 depicts a perspective view of a hooked
clip with a flexible curved clasp clipped onto a shaft of a movable or
non-movable object;
Figure 4 is a partial view of the mobile grounding
device attached to a movable or non-movable object via a hanging conductive
cord;
Figure 5a shows a perspective view of a roller
which is wrapped with an elastic conductive or dissipative tubing in an
incorrect dragging position;
Figure 5b shows a perspective view of a roller
which is wrapped with an elastic conductive or dissipative tubing in a correct
dragging position;
Figure 6 illustrates a partial view of the notch of
the clamping holder of the mobile grounding device; and
Figure 7 depicts a perspective view of the mobile
grounding device attached with a brush.
Description of the Preferred Embodiments
In the following detailed description, numerous
specific details are set forth in order to provide a thorough understanding of
the invention. However, it will be understood by those of ordinary skill in the
art that the invention may be practiced without these specific details. In
other instances, well-known methods, procedures and/or components have not been
described in detail so as not to obscure the invention. Reference will now be
made in detail to the preferred embodiments of the present invention, examples
of which are illustrated in the accompanying drawings.
Figure 1 shows a mobile grounding device (10) from
a dragging position to a rolling position in accordance to the preferred
embodiment of the invention for use with movable or non-movable object to
dissipate static charge to the ground. The mobile grounding device (10)
includes a roller (11) provided with an aperture (22) at both opposing ends of
the roller (11) for receiving a clamping holder (12), whereby the clamping
holder (12) can be easily attached to a movable or non-movable object (13) for
dissipating static electricity of the movable or non-movable object (13) to the
mobile grounding device (10) and then to the ground as shown in Figure 4.
The clamping holder (12) comprising an elongate
handle portion (12a) having a notch (14) located at one end and the opposite
end extended with a pair of clamping arms (12b) where both arms (12b) are
spaced apart with the ends fixed into the respective apertures (22). The
details structure of the notch (14) is shown in Figure 6. The clamping holder
(12) is secured onto the roller (11) through the clamping tension force exerted
by the extended clamping arms (12b) yet allows the roller to be freely
rotatable against the clamping holder (12).
The roller (11) is made of conductive material and
preferably made of metal. The weight of the metallic roller (11) provides
adequate gravitational pressure exerted on the floor while movable along with
the attached movable or non-movable object (13) to achieve good electrical
contact between the grounding roller (11) and the conductive or dissipative
floor.
The mobile grounding device (10) of the present
invention can be attached to the movable or non-movable object (13) via a
hanging conductive cord (15) to achieve a free-moving grounding system as shown
in Figure 4 or a hooked clip (16) to achieve a chainless grounding system as
shown in figure 3. The hooked clip (16) is formed with a catching member (17)
at one end for fastening to the notch (14) of the mobile grounding device (10)
and a flexible curved clasp (20) to be clipped onto a shaft (21) of the movable
or non-movable object (13). This will provide a simple and secured attachment
and uniquely simplify the electrical connection between the movable or
non-movable object such as a trolley, chair or a cart and the mobile grounding
device (10) without the use of a metallic chain. This technique will allow the
user to position and align the location of the grounding device (10) accurately
and precisely in the movable or non-movable object (13) to achieve a more user
friendly or benefit design in the transport system.
The 'long neck' of the elongate handle portion
(12a) or 'long claws' structure design of the extended clamping arms (12b) acts
as a pivotal lever to provide 'ease of turning' for a smooth drag whenever the
roller (11) is resting on an unfavorable position such as when the roller (11)
is resting with its axis along the same moving direction of the movable or
non-movable object (13) as shown in Figure 5a. The unique 'long neck' feature
will allow the roller (11) of the grounding device (10) to smoothly and freely
move in all directions without any jerky drag in any resting orientation of the
grounding device (10). No ball bearing, screw, bolt and nut, adhesive or rivet
is required in such unique 'long claws' design that can be easily and quickly
attached onto any bar-like or rod-like structure.
Optionally, a conductive or dissipative elastic
tubing (18) as shown in Figure 2a or at least one replaceable conductive or
dissipative elastic bands (19) can be applied onto the roller (11) as shown in
Figure 2b. This is to ensure that the turning or rolling of the metal roller
(11) is less noisy during use. At the same time, the elastic soft surface helps
to improve the electrical contact between the roller (11) and the conductive or
dissipative floor especially those floors with 'vein' type of conductive
lines.
The replaceable conductive or static dissipative
elastic band design is extremely user friendly. Replacement of the worn out
conductive or dissipative elastic band can be done simply without any
mechanical tool at all. This feature is unique compared to all the prior arts
as the maintenance and replacement work of the grounding device invention now
becomes a simpler and easier job.
Optionally, the metal roller (11) can be mounted
with a brush (35) on its clamping holder (12) as shown in Figure 7 to
automatically clean its turning surface during rotation movement. This is to
ensure that no dust or dirt deposit built up on the roller surface which can
affect the electrical property of the conductive or static dissipative roller
during use. The user friendly slot it brush (35) can be easily taken out for
quick cleaning.
This invention achieved a very simple and low cost
solution to provide a detachable, abrasion-free, movable in all directions
grounding device (10) to effectively drain static charge from movable or
non-movable object (13) to ground which the prior art failed to addressed.
As will be readily apparent to those skilled in the
art, the present invention may easily be produced in other specific forms
without departing from its essential characteristics. The present embodiments
is, therefore, to be considered as merely illustrative and not restrictive, the
scope of the invention being indicated by the claims rather than the foregoing
description, and all changes which come within therefore intended to be
embraced therein.