The present invention relates generally to electrostatic control device, more particularly to grounding device for dissipating electrostatic charges accumulated on a structure.

BACKGROUND OF THE INVENTION

Electrostatic is an electrical charge at rest created mainly by friction of movement causing an imbalance of electrons. The magnitude of static electricity depends on factors such as the type of material, speed of separation, contact pressure, and relative humidity of the environment. The sudden discharge of static is called an electrostatic discharge. Some electronic device cannot withstand electric spark discharge which may permanently damage the device. As more transistors are crammed into electronic device, the more fragile the device behaves towards electrostatic spark.

Care is taken in manufacturing and handling of electrostatic discharge sensitive components to reduce, or hopefully eliminate static electricity. People, equipments and materials have to be properly grounded to discharge harmful static charge that may reside on every people, equipments or materials.

Equipments such as mobile carts which are used to transport electronic equipments can cause static electricity to discharge and damage electronic components. Metal carts have to be connected to ground by grounding devices such as chain dragged underneath the cart or conductive wheels. Drag chains have little contact with floor in reality and become disconnected with ground especially on patterned conductive tile or static dissipative tile. The free end of the chain may bounce off the ground when there is robust movement.

Typical conductive or static dissipative flooring used in electronics industry consists of conductive plastic square tiles commonly joint together with plastic joining rod using hot weld process. Crack lines appear on the floor due to aging which causes uneven floor surface. Patent application US 2003107195 describes an electrostatic dissipative cart comprising a cart body that is grounded with static dissipative material such as polypropylene and nylon.

A grounding device described in Malaysia patent MY 126078 provides a means to drain static charge from a target to ground. It comprises of a unitary piece of planar conductive sheet material to drain static electricity from a target to a weight. The weight is in a form of bar resting on a grounding surface. The weight is considerably heavy enough to be always in contact with ground. In the form of a rolling bar, the weight has limited surface area contact to ground and rigorous movement of the bar does not ensure a good contact with ground. Furthermore, the highly mobile nature of the rolling bar is difficult to manage, making it impractical to be used as a grounding device underneath targets such as cart, trolley, chair, etc.

In the form of a planar bar, the weight has large and constant contact area with ground. However, such weight is more suitable for targets which are stationary or involves little movement. The movement of the planar bar is restricted when it is obstructed by an obstacle caused by uneven surface. Hence, the weight might be stuck at the obstacle. If the target is moved further the conductive connecting sheet might break. Furthermore, the edges of the bar can cause severe damage to various objects during accidental collisions with such obstacles.

People having ordinary skilled in the art would logically select and improve the planar bar grounding device by cutting a pitch along all its perimetric edges in order to surmount uneven floor. However, such an improvement would result in uneconomical modifications as a typical square bar have six surfaces and twelve edges to be pitched. Furthermore, a ground bar with such features is more costly to manufacture and takes a longer time to produce.

It is desirable to have a durable grounding device which is easy to manufacture, low cost and freely movable in all directions without any restriction while effectively dissipating electrostatic charge from a moving target to ground. This gives rise to further research and development on grounding device. SUMMARY OF THE INVENTION

The invention consists of a small palm-sized weight which can move in any direction freely along a flat conductive or static dissipative grounding surface. A unique disc shape weight is disclosed in this invention.

The invention is conceived to provide a movable grounding device which is trip free even during intensive movement of a target at uneven floor. The edges of the weight are universally pitched so that the weight can easily surmount obstacles along its path in all directions. The weight has a stable broad base area so it will not flip or roll over during movement of the target. Such invention is good for both stationary and movable target application to achieve maximum utilization.

The invention also encompasses the design of a grounding device with considerable weight and relatively high surface contact area at the base of the weight so that static electricity is reliably dissipated to ground.

The uniqueness of the invention also lies in the collision-friendly design. The invented disc-shaped weight has no sharp edges. Such unique design will result in minimal damage during accidental collision with obstacles.

The further technical advantage of the invention is that the disc-shaped weight of the grounding device is a one-piece universal design without any attachment or joining part which is ideal for robust and long term heavy duty use. Thus such grounding device practically requires no repair & maintenance cost.

In summary, a novel and unique grounding device which is collision friendly, simple to make, low cost to produce, a one-piece robust and durable design, freely movable in all horizontal directions without restriction while effectively dissipating electrostatic charge from a moving target to ground is hereby been researched and strategically invented.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail, by way of an example, with reference to the accompanying drawings, in which: Fig. 1 illustrates a perspective view of a first embodiment of a movable electrostatic grounding device according to this invention;

Fig. 2 illustrates a side view of the movable weight;

Fig. 3 illustrates a top view of the movable weight;

Fig. 4 illustrates a profile of an uneven floor surface;

Fig. 5 illustrates a perspective view of the weights moved along the uneven floor surface; and

Fig. 6 illustrates a perspective view of a second embodiment of the movable electrostatic grounding device.

DETAILED DESCRIPTION OF THE DRAWINGS

A first embodiment of a movable electrostatic grounding device is described according to Fig. 1 , showing a conductive strip (22) having one end connected to a target and the other end connected to a weight (26). Equipments or objects which need to dissipate static electricity are target of the device. Static electricity is dissipated from the target, especially moving target through the conductive strip. Moving target refers to moving equipment such as chairs or carts. The weight attached to the other end of the strip will dissipate the static electricity to ground when weight is in contact with ground. The weight is connected to conductive strip with an attaching means (24).

The weight (26) is constantly touching ground due to gravitational force. Fig. 2 and Fig. 3 portray the weight having a shape of a disc. The base and top surface of the disc is desired to have a large contact area with ground. The weight is desired to have a radius, r more than twice the height, h of the weight. The mass of the weight is considerably heavy so that the base surface always maintains good contact with ground. The disc shape weight effectively dissipates electrostatic charge when the weight is dragged around.

The edges (28) of the disc are pitched to an angle. The edges are pitched so that the weight (26) can surmount obstacles in its path. The weight does not flip or roll over when it is dragged around. The pitch can also overcome any knock-on obstacles along the path of uneven floor. This will eliminate any jerking when the weight is moved around. If the weight is stuck, than the forced movement of target will break the strip. Furthermore, the unique disc-shaped design has no sharp edges in either stationary or moving utilization that will result in minimal damage during accidental collision with obstacles.

A practical weight (26) shall easily fit the palm of a hand. Typical size of the weight can have a radius, r of 10 mm to 50 mm and a height, h of 4 mm to 20 mm. A preferred weight can have a radius, r of 25 mm and a height, h of 10 mm. The weight is pitched along the edges of the disc by a ratio x:y of which x is the horizontal distance of 5mm from the edge and y is the vertical height of 2mm from the top rim. Hence the pitch has an angle of arctan (2/5) or 21.8° relative to horizontal plane. A preferred range of pitch angle is 20° to 40°.

There is at least a hole (30) on the weight (26) so that it can be connected to a conductive strip. The hole is located at the pitch having a preferred radius of 1.75 mm.

An attaching means (24) connect the weight (26) to a conductive strip (22). The attaching means may be in the form of a hook or a split ring with two open ends. The attaching means using split ring are similar to attaching means used in key chains. The attaching means attaches to the hole of the weight. The attaching means shall also be conductive to allow transfer of static electricity to weight.

The conductive strip (22) acts as a medium to allow transfer of static electricity from target to weight (26). Any material which transfers static electricity can be used as conductive strip. Metal chain, metal wire, metal spring or braided metal wire make a good conductive strip.

Fig. 4 shows a cut-away pictorial profile of typical flooring used in a static sensitive manufacturing environment. Tiles are commonly joined with joints (32) on each side of the tile which remains intact initially. Chips and debris (34) underneath the floor creates protruding spots (36). Cracked lines subsequently form on the tile joint as a result of shrinkage of plastic tiles. The shrinkage resulted from factors such as temperature changes during use and aging. Fig. 5 shows the weights being moved along the uneven floor surface. For a weight having the shape of a bar, the weight can be obstructed (38) by uneven floor surface. For a weight having the shape of a pitched disc, the weight is optimized to surmount (40) uneven floor surface. At the point of impact at the protruding spots, the pitched disc can surmount better than a bar.

Fig. 6 shows a second embodiment of movable weight (26) having two conductive strips (22). The conductive strips are connected to weight with conductive attaching means (24). A weight with two conductive strips attached to two holes on the weight will facilitate a more stable movement of the weight compared to the attachment of having only one conductive strip spaced apart. Thus forward, backward, left and right movement of the target will not cause the weight to move relentlessly when it is connected with two conductive strips spaced apart. Two conductive strips will also provide better grounding durability because if one strip breaks, another strip will still be dissipating static electricity. The second embodiment will have a more lasting and durable movable weight system than first embodiment.

Accordingly, the invention has a simple setup of grounding a moving target with a movable grounding device. It is the combination of the above features and its technical advantages give rise to the uniqueness of such invention. Although the descriptions above contain much specificity, these should not be construed as limiting the scope of the embodiment but as merely providing illustrations of some of the presently preferred embodiments.